I played several games but the one that stands out the most to me is Star Trek: Voyager - Elite Force. EF was based on the Quake III engine (idTech 3) and came with QERadiant, amongst other tools, that let you make your own maps for it. The story for the game was awesome and it was the first game that I think did justice to the atmosphere present in the show with only a little bit of the cheese. Once I finished the game, I went right into making my own levels for it. It was really amazing. I miss games like that and the fact that they came with the editing tools for them.