The whole of the game is that you're a user-generated merc sneaking around on a base (Basically Metal Gear Solid 1). There are tools, like C4s and USPs and stuff like that. The main gimmick is that there's a leaderboard, and your score and grade place you on the board, so you keep replaying the game to get to the top. There are no checkpoints, but there is a profile system in place.
Maybe I'll get started on this :)