Underappreciated Martyrdom Zealot
 Zealot Build - Warhammer 40k: Darktide 

This build is a Low health build, the lower the better, Zealot has a lot of under appreciated stuff in their kit that lets them get in and out of situations that other classes could only dream of being able to, with their Fury restoring toughness to having a whole perk that just says no to death that also heals you up to a whole wound and a half, this class has the potential to be really strong but also really goofy

My setup revolves around the Martyrdom perks giving a ton of resistances and damage when you have low HP. with the way I spend my perks I am left with one extra point that I use as a flex slot to swap around based on the weapons I use and the mission type. I personally love the Devils Claw sword for its insane ability to parry literally any melee enemy including crushers and even the three mutated minibosses the only exception is grab attacks which are easily avoidable with dodging, which you SHOULD DO A LOT literally everything can be dodged and with the game not needing stamina for dodges to activate this allows you to run circles around everything, including Pox Bursters who struggle to keep up with you if you space them right, I will go more in depth as to the weapon choices below

For fluidity sake I'm going to group terms together, 
Enemies that would pin you down such as Mutie's Trappers and The Beast of Nugle swallow attacks I will call grabbing, 
Heavy hitters such as Sniper's, Crusher's Overheads or Maulers I'll just call Heavy hitters
Enemies that are more oppressive or good at area denial such as Flamers, Grenadiers or even Ragers to some I will just call Oppressors

I am admittedly very biased with weapon choices. I feel like my choices here will cause some controversy, however I do not care because I find these to fit my personal play style the best. I will  however give alternate options with perk choices to go alongside them because I understand not everyone plays how I do or likes the same stuff I do.
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Perks and the extra point
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So as I stated earlier there is indeed an extra point, with this set up you can front line with purely your melee weapon and as long as you are aware of trappers, dogs and mutants you are pretty much unstoppable, that being said there are some perks that make things WAY easier for your survivability or dishing out more damage

Second Wind: this perk is nice but not needed, it really helps with Toughness gen if for whatever reason you are getting hit enough for this to be a problem, with how often you SHOULD be dodging this will activate almost every time you hit the spacebar, just make sure you dont tap W by accident otherwise the game will make you jump instead which could get you downed or grabbed. Plus its a great tanking tool when dealing with Oppressors on top of your typical hordes or ogryns.

Thy Wrath be Swift: This perk is pretty nice as well, especially when you are surrounded, HOWEVER this perk is mostly useful to get out of a bind, seeing as you gain a 15% movement speed on taking damage.. Personally Martyrdom is already more than enough plus the stun resistance is only really good when you get hit by a heavy hitter or you are trying to use your gun.

Against all odds: This perk is REALLY GOOD, the only reason why I didn't pick it for the core build is because half of it is kinda pointless. given this game has a lot of hoards its very tempting and very strong to use, however the cleave damage is kinda meh depending on weapon choice. Most of Zealot's melee weapons already get an insane amount of Cleave to the point where taking this perk is only useful for the added damage it gives.

Unrelenting Fury: This one is for ability gen, its nice but also not mandatory, if you want to spam fury a lot go for it :)

Scourge: Honestly this one feels like a nothing burger most of the time, You end up one to two shotting most enemies anyways, the only time this one matters is against heavy hitters and bosses. which is nice but there are also better options

Prime Target: this one I considered adding because its really good, however i find that the elite toughness gen isn't that great since its an over time and not a burst gen. Not my favorite but hey try it yourself and let me know your thoughts :)

Unfaltering: This is amazing if you are a heavy attack enjoyer, I however am not a heavy attack enjoyer, I find the tradeoff to be very unrewarding and tend to go down way more when I use heavy attacks. use this if you heavy attack otherwise anything else is great :)

Time to Kill: This perk is another situational one, Its absolutely amazing against tanky enemies and bosses but kinda bad against anything else, it also requires your allies to pull aggro. So unless you can consistently give backshots to the Plagueryns this is a meh perk.

Riposte: This perk is really good and one I recommend right next to Second Wind, that stacking damage on dodge is really good and builds fast. There really isn't much else too it than that.

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Melee
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Devils Claw sword:
Any Mark
Perks: 25% Damage (Unarmored Enemies) / 25% Damage (Unyielding Enemies)
Blessings: Rampage / Shred
This thing is really strong despite it being a starting weapon, it has really fast swings and surprisingly high damage for a light spammer. plus this weapon has one of the most overpowered things in the game, Zero cost blocking. The ability this weapon has is stupidly busted as it is able to not only block every melee attack in the game but also immediately follow up with a high damage riposte that clears hordes and absolutely mulches melee bosses like they are nothing. The only issue this weapon has is the parry is tied to SWING SPEED meaning if you have slow swings its going to struggle against a fast enemy like the Daemenhost. if you run this weapon you can literally solo Daemenhosts as long as you are the one to awaken them, just make sure your team handles the horde around you otherwise you may get grabbed.

Relic Blade:
Mark X for crowds, Mark 2 for single target or heavy attacks
Perks: 25% Damage (Unarmored Enemies) / 25% Damage (Unyielding Enemies)
Blessings: Cranial Grounding / Heatsink
This weapon is really strong and if I'm not mistaken considered one of the meta weapons, and for good reason, Running Mark X is amazing for clearing crowds with a heaavy hitting single target heavy, and the Mark 2 is a nice crowd clearing heavy, however I only use this when I am running low level missions with friends due to the lack of a parry, the ability is really strong, adds shock damage which stuns enemies and grants more damage for your carnage. This is one of those weapons that is amazing for a heavy attack enjoyer.

Heavy Eviscerator
Any Mark? (I really don't like this thing so I don't know)
Perks: 25% Damage (Unarmored Enemies) / 25% Damage (Unyielding Enemies)
Blessings: I'm not really sure truthfully.
So quite honestly I don't really know how to build this thing, It isn't very great for crowds however it is really good for keeping heavy hitters in place. Its gimmick is a high damage strike against a single target.. and in a horde game that isn't really great in practice.. yet somehow this is the go to for meta builds for some reason? I don't understand it myself but oh well. its unique blessing is really hard to get off when you have allies hitting the same target as you since it seems to only activate when you get the final hit with your ability. If someone could explain how to build this thing please do and I will adjust this part of the build

Shock Maul
Mark: Agni Mark 1a
Perks: 25% Damage (Unarmored Enemies) / 25% Damage (Unyielding Enemies)
Blessings: High Voltage / Opportunist (Use Thrust for heavy attack enjoyers)
This weapon is more of a support weapon with its ability, Its pretty good normally however when you fight anything without a boss health bar you can pretty much keep them still indefinitely or until they are dead, use this against crushers or reapers and let your team take them out :) that being said the blessings are 100% there for bosses that font get stunned by this thing.

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Guns
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Spearhead Boltgun
Mark: Locke MkIIb
Perks: 25% Damage (Flak Armored Enemies) / 25% Damage (Carapace Armored Enemies)
Blessings: Cavalcade / Inspiring Barrage
This weapon is really powerful. I mean hell its the boltgun, why would it not be, that being said this weapon is not used as your primary source of damage, sadly its small magazine size and low ammo reserve make that painfully obvious, its core use is to soften up single targets like bosses and ogryns as well as gaining the blessing buffs, the critical chance from Cavalcade carries over to your melee for the 5 seconds which can be really handy against bosses.

Purgation Flamer
Mark: N/A
Perks: 25% Damage (Unarmored Enemies) / 25% Damage (Unyielding Enemies)
Blessings: Showstopper / Penetrating Flame
This weapon in my opinion is very volatile to use, I don't think its bad but it just feels awkward. Its primary fire is decent at keeping enemies away from you and its secondary fire is the flamethrower, you shouldn't commit to the secondary fire unless you know you are near your team and they will cover your rear because the MOMENT you get hit by anything and you will get knocked out of your firing. (unless you run Thy Wrath be Swift), this is another weapon I enjoy on low levels but I do see others use it on higher levels now and then as well.

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Relics
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This one is pretty straight forward and also tends to flex around play style, with the perks alone you get 5 wounds which nets you up to 4/5 stacks for Martyrdom so running a relic with an extra wound will top your perk off, alternatively you can run all toughness relics and not really care about the final stack. that being said with how I play the game I tend to also have a flex slot on all my relics as a result but I can give suggestions for that slot with the alternate relic setup in mind

3x Toughness relics:
Perk1: 20% Damage Resistance (Gunners): This Perk applies to Reapers too, I have done pretty extensive testing on this and noticed a drastic damage difference when running this, It also seems to be the ONLY perk that resists two types of enemies
Perk2: 4% Ability Regeneration: More fury's means more damage and toughness gen
Perk3: Flex Slot

2x Toughness 1x +Wound
Perk1: 20% Damage Resistance (Gunners): This Perk applies to Reapers too, I have done pretty extensive testing on this and noticed a drastic damage difference when running this, It also seems to be the ONLY perk that resists two types of enemies
Perk2: 4% Ability Regeneration: More fury's means more damage and toughness gen
Perk3: Flex Slot (5% toughness on wound relic, nice but optional)

For the flex slot you can put as you wish however I would recommend the additional toughness for a total of 15% toughness, its really nice to have
Other perks that are nice for this build include

15% Corruption resist, Stacking to 45% tie this with the 40-50% additional resistance martyrdom can get you pretty much unable to gain corruption

12% revive speed: this is nice if you aren't confident in your team, stacking up to 36% you can get your allies up fast, do note this does not apply to freeing from trapper nets.

30% Toughness Regeneration speed: This is meh considering the speed only counts when you aren't taking damage, this does not seem to apply to regen perks at all, take it if you really feel this will be beneficial to you

Any reward perks: these are nice for farming but don't give practical benefits in combat

Any resistance perk: the nice thing about these perks is they stack linearly and all give 20% so if you really hate a type of enemy then pick that enemy to be able to ignore :)