Mine is definitely Tomb Raider 2, I pretty much grew up with it ever since my step brother let me play because he sucked. The environments are exotic and I will never forget the sunken ship, the puzzles were confusing and the Opera House was one of the most infuriating but satisfying levels I have played. I owned the majority of the original Tomb Raider games and I have never actually beaten one myself, so I set out to change that recently by buying them all on Steam.
So whats yours and why?