tl;dr if you like firaxis XCOM gameplay or squad games in general and you like the 40k aesthetic then this is a solid pickup.
You are the silent commander of a company of Grey Knights, the Space Marine arm of the Inquisition specializing in dealing with Daemonic threats. On your way home from another campaign your ship is commandeered by an Inquisitor to combat a newly discovered galactic scale threat. This is the setup for an xcom-style game set in 40k where you send 4-unit squads on turn-based tactical missions.
The game never stopped being fun for the whole 60 hours even if this kind of game does get repetitive. The way they did that is to make your units into total badasses who can wade through enemies even in early game. Mastery of the various mechanics rewards you with even more satisfying gameplay like chaining extra turns to mow down even more grunts. That's not to say there isn't any challenge involved but most of that is less about whether or not you will win but in how cool you can make your victory. Some story missions and boss fights might need to be played more than once until you figure out the right combination of builds and gear to get through them. I played on "normal" difficulty which felt about right.
Your units are each specialized classes with their own talent trees, some are better than others but none are useless. Later in the game you get "advanced" classes but imo it happens too late and other than the Librarian with his strong AOE none of them are particularly better than the base ones. It will take a bit of experimentation to find which of the talents you ilke best and which you think are crap, and unfortunately respeccing is fairly expensive.
A couple of mechanics stand out compared to XCOM. First there is no miss or (base) damage RNG. All shots always hit, but range, cover and special abilities can decrease damage. The RNG exists in the form of critical hits but those are strictly bonuses and iirc the enemy doesn't get them. There is more focus on melee and mobility and because your units are all tanks there isn't nearly as much emphasis on always moving between cover. Second your team's action points are restored when you enter combat. That way you don't have to worry about discovering the enemy with your last move and effectively giving them a free turn. One notable mechanic is the "stun" where enemies have a stun value that decreases each time they take damage or from specialized stun attacks. Once it hits zero the enemy is stunned and takes a guaranteed critical hit from melee. Small enemies can be executed when stunned which gives your whole team an extra action point which can lead to the aformentioned extra turn chains.
The strategic level isn't particularly interesting where you choose in which order you build various base upgrades, adjust your team's gear and recruit new units. The gearing UI is a bit clunky but adequate. One tip is to upgrade your ship's engine's twice before starting the Craftworld mission, you will need that speed afterwards. The reason you need the speed is each mission has a strategic time limit that is consumed as your ship travels and the map is large enough that you can't make all of them and have to choose.
The missions reward you with "requisition points" which you can spend on recruiting, respeccing, or loot. Each month you can also spend your requisition points on upgrading the chance of better loot in each category. This makes for interesting choices in the early and midgame about whether to save your points for better potential loot or to spend them on making your squad better now. It also means that you are a bit at the mercy of RNG because some gear will really make your life easier if you happen to get it earlier.
In addition to the missions there are events which require you to make story choices that give your ship, squad, or resources various bonuses or penalties. Unfortunately the developers made the decision to not tell you the game mechanics effect of each choice so either look it up on a website or go in not knowing exactly what you are going to get.
The story isn't anything really groundbreaking but it isn't gay. Though one of the main characters is female and seems eyerollingly smug at first she is well written and gets more interesting as the story progresses. Actually another of the 3 main characters is female but she is a Tech-Priest of the Mechanicum so she probably replaced her cooter with a co-processor or something and it never matters for the story.
Overall I enjoyed it a lot and while most missions were cakewalks there was occasionally enough clench factor to make for satisfying gameplay sessions.
The thing that I hate the most about Chaos Gate is that its only Nurgle, they blue ball me with Bloodletters at the start, I get to play with daemon slaying Gray Knights then I ONLY get to purge Nurgle.
Space Marine 2, bet its going to be front loaded with nids then its going to whiplash me with fecking Nurgle again.
I liked Chaos Gate, couldn't finish it due to Nurgle fatigue, and being disappointed there wasn't at least some Khorne red bois to banish back to the warp.
You play the original 40k chaos gate? it's khorne and tzeentch all around. Not a single nurgle thing in there