I'm sorry, but the core games (Zelda, Mario, Mario Kart, etc) are worth the price of the Wii alone. From a gameplay standpoint, Nintendo has always been head and shoulders above the rest. Sure, they don't have the same depth of library that other consoles have, but the exclusive games they do have make the system a must for me, especially at that low price point.
Yeah, I'm with Derek. The Wii works well for me because I'm more of a social gamer. I don't really sit by myself playing games, online or single play. Although, I'm playing Madden 08 on it right now, and it really isn't bad. I haven't played it on PS3 or 360 so I couldn't really compare, but I'm having fun. A few games stick out for me:
SuperMario Galaxy: Awesome game. I played this for hours. My two boys, age 5 and 3, sat with me for hours just watching me play, telling me where to go, what to do.
Mario Party: Not exactly my cup of tea, but my kids like to play it with me, and it's fairly fun with friends over.
Mario Kart: Best multi-player racing game, period.
Wii Sports: Very simple games, but they still entertain me.
Madden: Don't like the Madden interface as much as I used to, but that's not a function of console I suppose.
I'm in the middle of a major remodel, so I don't have a lot of gaming time. But when I'm done, I can see myself wanting a 360 or PS3. I played Gears of War and COD4 with some buddies, and it was AWESOME, even though I hate playing shooters with a control versus a mouse and keyboard. When that comes, I'll be sure to start World War 3 here by asking what I should buy: PS3 or 360.