So much good have been said about this, so I'll just repost what I wrote about it in my blog a few months back.
Beyond Good and Evil (2003) is considered a great game and somewhat of a classic, but it never became a commercial success. I am not going to give you a review, most gaming sites have one. I am not here to give you facts about it either, for that you can read a rather good article about it on the domain of questionable knowledge (wikipedia).
I am however saying that if you have never played this game, you have missed out! Get a hold of a copy for your PC, PS2, GameCube (compatible with Wii) or Xbox (not 360 compatible) and I promise you that you will not be disappointed, except for the fact that it did not get the sequels that were planned (although one seems to be on the way now).