Very similar to Doom of course, but even within the realm of early shooters it's very similar, visually almost identical in a lot of ways. Similar gameplay wise too, so basically the thing separating it is the genre or plot, less demons from hell in futuristic space and more evil zombie cultists in a strange version of the world with 1000% cheesy 80s slasher influence and the best cutscenes ever. Seriously love the cutscenes, they're so crap in today's standards but I love them so much. I love this game generally, it's absolutely cheesy and silly-edgy but I love that and I love the setting and the atmosphere and the cultism. I heard it was a tough one, but I had an easier time with it than both Quake and Doom II, but then again perhaps I got good.