I love my Wii because there's loads of good, unique titles for it, especially if you consider the back catalog of the Gamecube. I own a PS3 and a gaming PC, but my Wii still gets played on regularly. In particular, there are multiplayer titles on the Wii that are very accessible to whatever company I have, can be played by four people in the same room on one console, and don't have good analogues on other systems. Rail shooters are especially good (Ghost Squad in Paradise Mode is hilarious in a group).
The list of games I've enjoyed because of my Wii is pretty huge: Muramasa, Twilight Princess, Ghost Squad, Okami, House of the Dead 2 & 3, Trauma Team, House of the Dead: Overkill, No More Heroes, Super Mario Galaxy 1 & 2, Lost Winds, Metroid Prime Trilogy, Tales of Symphonia: Dawn of the New World, Fire Emblem: Radiant Dawn, New Super Mario Bros, Super Smash Bros. Brawl, Endless Ocean, Mario Kart Wii, Elebits, Super Mario Strikers, and Boomblox. I've also played a few Gamecube titles on it: Eternal Darkness, Tales of Symphonia, Mario Golf: Toadstool Tour, Pikmin 1 & 2, Windwaker, and Mario Power Tennis. That's over two dozen titles, and I'm sure there's more worthwhile games out there that I haven't played
Good, fun games matter to me more than the sheer power of a system. I love my PS3 too, but my Wii has been played on for way more hours. Sure, there's a lot of crap Wii games on the shelfs. I don't buy them. The good titles are still good and make the system worthwhile. I understand it's limited in terms of graphical power and online capabilities, but that's what my PS3 and PC are for.