Had a Wii at the beginning of the year and moved it on as there was nothing around for it. Now there's Mario Galaxy, Paper Mario, both Resi Evil games, Mario/Sonic Olympics etc I've bought another. Thoroughly enjoying Galaxy so far. Makes a change to the kind of stuff I've been playing on the PS3/360.
At the end of the day, if you can afford more than one get a Wii AND either PS3/Wii. If you can only get one, then I'd currently advise against the Wii as a sole console.
Simple as that really, hope it helps.