Spelunky feels unique in that, whilst being a multiple floor dungeon run type of roguelike, it surpasses the average game of the genre by having a lot of variables in it (and i don't mean potion effects). There's different variants of levels, different types of levels you can access on each floor...SECRETS! The game is built on secrets! What seems at first to be maybe a simple but fun indiana jones simulator turns into a game that has a lot more depth than you first thought. The world of Spelunky is always interesting and dynamic and for that I have to give it a buttload of credit cus it's what makes this game timeless and replayable even 7 years after first playing it.