I'm going to have to go for the Prince of Persia Sands of Time trilogy. A very strong series of games. The first is an absolute classic - outstanding gameplay, great story, beautiful to look at. The platforming and the flow of the movement is brilliant. The combat isn't great, but it's good enough. I've completed this game so many times. The sequel, Warrior Within, suffers from a stupid emo gothic change in tone, with ridiculous blood and gore and paper thin female characters with their boobs hanging out, but that's offset by the fact that the level design and structure of the game is even better than in the first game. The combat is massively over the top and I could do without it, but I'll put up with it for level design like this. The third part, Two Thrones, fixes the tone and visual aesthetic, and the combat is a bit more manageable, though the level design is waning a bit by this point. It's still good, but not as good as it could be. So diminishing returns as you move through the series but when you've started so strong, even a bit of a drop off leaves you with a game worth playing at the end of it all.