As a devoted PS3 fan i was so supprised how much fun this console is. Sure it won't do anything like the stuff the PS3 can do but this is aimed at a different market. The family market. It is a great game system to get everyone together and interact. In contrast to the PS3 which is primaraly focused for individual play (with multiplayer interaction coming form online play).
I've just been playing on the Wii Fit and i must say apart from it calling me overweight, (ok, i've put a stone on recently writing a thesis) i really enjoyed it. As for the other games, i do see a short shelf life, especially after mastering the game/wiimote control. But with games super cheap, who can complain.
The Wii is a fun system, but nothing more that a second/family game system, but obviously if raw gaming power is what you are looking for then have the PS3 as your main system