I really am getting bored - although i do realise that everyone is entitled to an opinion yada yada yada - of hearing the Wii is "great for group games only, or when your mates are round" type answers, because I dont think this has been mentioned in this thread:
The Wii does not have that many AAA titles, and in all honesty it wont ever get as many as the 360. However thats not the point. When a title DOES come out that has properly used the hardware graphically, and has controls designed from the floor up for Wii that is intuitive and imaginative, then the experience of this - in a single player game too - cannot be matched, simply because no other system does games the way Wii does (with this control mechanism).
If its gonna be your primary system then, probably get a 360 - if you already have other sources, say a PC, then get a Wii. You may not buy games that often, but when you do get one - it will be a fantastic experience.
But the problem is that you cant expect it that often right now. But with the amount of consoles sold, the Wii is becoming less 'oooh new and controversial' and more 'oooohh, lucrative' which can be good if it means more dedicated dev teams for Wii - instead of the PS2 port teams we get now. Its still a maturing console remember.
Just buy a Wii - unless you need 'shiny' games :)