Thematically, Darkwatch is like Vampire Hunter D meets Evil Dead. In terms of gameplay, it's basically a '90s FPS (particularly seeming to take a lot of "inspiration" from Blood), updated for Dual Shock 2-stick controls.
You play as Jerko Cross, a train robber ... OK forgive me but I gotta stop right here and mention the story is really, really stupid and leans heavily on nonsense contrivance. The first level is Jerko singlehandedly robbing a train ... but then he sees the train is full of the undead ... and decides to keep going. Then further decides that opening some glowy vault that this chick just warned him not to open will somehow lead to golds and not undead plague. It never really makes more sense than that as you go. Just repeat to yourself, it's just an oldschool FPS, I should really just relax.
Anyway. An "undead" theme means, naturally, Bullet Sponge and Endless Respawn enemies, which is part of what earns the game the 2/5. There's also very few types that are spammed over and over, naturally rising from the ground and materializing out of thin air endlessly. There's the skeletons that mindlessly charge you and swing various farm implements, the zombie gunslingers with ridiculously good aim for dudes lacking cartilage, floating banshee women that are slightly more interesting but also much rarer, and a shit-talking fat guy with swords that amusingly becomes totally helpless if there's any sort of ledge around for you to stand on. The gunplay isn't all that satisfying due to the sponginess, the suicidal charge AI of the enemies, and aim that's a bit too imprecise given the hordes you're being regularly asked to hold off.
The game is almost totally on rails, it's almost more like a House of the Dead game where you can freely move about within tiny little zones one at a time. Come to think of it, that might be what they were going for. Anyway, it has one of those ultra-simplistic "moral choice" systems too. Every now and then some random citizen will pop in from out of nowhere, and Jerko gets a choice, literally titled GOOD or BAD. Ex: "GOOD: Ease the woman's suffering. BAD: Drink her blood, you selfish cunt." These choices earn you either good or bad powers, but the good powers are so much better the game really gives you no other reason not to choose them other than experimentation, or if you get off on cruelty.
One thing that should be mentioned is that the soundtrack is perhaps the most shameless Ennio Morricone ripoff I've ever heard. The title theme is literally the title theme to The Good, The Bad, and The Ugly, apparently changed just enough to avoid lawsuits. The song in the horse portion of the opening level is also awfully close to the theme of Fistful of Dollars. I suspect this isn't "tribute" so much as "lazy hack composer looked up the most popular Spaghetti Westerns then copied the first track or two off their soundtracks." Really, it's pretty goddamn shameless. This is embarassing Capcom, talk to whatever little studio made this and tell them they need to get their own shit.
(Edit: Since posting this I've learned that they actually licensed the Good Bad & Ugly theme for use. I partially retract the hackwork criticism, but not entirely. Seriously, why license possibly the most iconic movie theme of all time? It belongs to that movie, not anything else. Still a classless move by all involved parties here.)
Darkwatch actually has a pretty neat look to it (despite obvious limited budget) and pulls off a pretty decent horror atmosphere. But it's also very unpolished, has lackluster drab game environments, less-than-satisfying gunplay, a really dumb story, and too much Romero School stuff like enemies spawning right next to you after a cutscene and killing you before you even know what's going on. Oh, and there's some obnoxious iffy platform-jumping segments here and there. On the whole I can't really recommend it despite good atmosphere and basically decent gameplay.