I really liked playing through Braid. It was short and used a unique play mechanic added onto a familiar genre - in this case, time control in a platformer. It makes a big difference to the way you play when, instead of dying and restarting the level, you just rewind time and try again. I was much more reckless and willing to try difficult or dangerous things, because progress is never really lost. It is still a challenge, though, because there are the time mechanism puzzles, playing with the concept and twisting your brain. Lots of fun, though I had to consult a guide for a couple of puzzle solutions. One in particular was the way a puzzle display in the background acted as an extra platform, and I just didn't notice.
The ending, the very final level, was where the real "wow" factor came in, though. I don't want to spoil it, in case you feel inclined to go and play it yourself, but it was, to me, the cleverest part of the entire game, and put a new spin on everything that came before. So do go and play it now.
Mokalus of Borg
PS - I realise this is not the newest of games.
PPS - I just wanted to say what I thought of it.