It's not just the puzzles that make the game experience. It's the combination of combat, puzzles and story, involvement in the game, that do it.
Best puzzle? I can't remember a lot in fact. I haven't made many really long single-player maps, mostly testmaps and such. As for my compo entry, the biggest puzzle there may well have been how to open that door that blocked movement to those 2 batteries... somewhere I've hidden a crowbar although not many have found it yet...