It felt like an expansion to Doom. The only new things about this game are a few new enemies and one new gun. I liked the inclusion of a final boss, which made it different from the other demons. I only played Hell on Earth, as that's what the game launched with. There's are some other expansion packs included in the game but there just extra levels. This game is pretty much Doom but with a couple of new features. I wouldn't recommend playing it unless you feel the need to.