Portal is the most memorable game I've played in months, maybe a few years, even. It's original, hilarious, innovative, it's plain crazy awesome.
The Challenges are tough, though. I finished about 3 Advanced Levels, but the challenges are crazy tough (especially the time challenges) and yes, I know the level exploits.
All in all, the game is worth playing no matter what side of the gaming spectrum you are. It's the sort of game we need more of.
Or well, I'll be content if we just have more songs like the unbelievably awesome one at the end.