One of the best horror games on the market.
The sound is creepy and builds up the tension.
The environment is great especially when the zero gravity kicks in.
Also when you're outside the ship, everything is so real: the space, the way Isaac moves and breathes.
The ammo is scarce but that is a good thing because it forces you to face you enemies up close. If you shoot any enemy without destroying their limbs, they will slowly come towards you while you're shooting like a madman. There are lots of enemies: disgusting , scary and beyond scary. The boss fights are cool and require some thinking.
The upgrades are useful and the weapons are fun to use giving you a sense of progression.
The graphics, lets just say that every screen shot can be used as a wallpaper. (ex. the bridge of Ishimura).
I bought a copy of this game knowing only that is just another horror video game. I ended up by loving every aspect of it.