Super Mario Galaxy is one of the best games to come out in years. The satisfaction and pleasure that I experienced with this game could probably only be compared to The Legend of Zelda: Ocarina of Time, arguably the best video game of all time.
Mario Galaxy's high point isn't its story-- you play Mario, and in an attempt to rescue Princess Peach, you meet up with Bowser at the end of the game. It's basically the same story in all Mario games with a few bells and whistles thrown in for extra measure. The graphics, while the best on Wii, still don't compare to the technical prowess of the other next generation consoles, although the art and maybe even some of the textures are definitely some of the best this generation.
The best part of this game is indeed the gameplay, and whether it's beating up Goombas, defeating a boss, or exploring the beautiful galaxies that this game has, it's an amazing experience. Overall, if you own a Wii, you must have this game. Some of the later levels and challenges might be a little difficult for younger players, but everyone in the family will surely love the core of this game.