I've greatly enjoyed Wii, more so then PS3, Xbox 360, and PC (if I don't take into account Plants vs Zombies, so good) so I say it's worth it. I've found it best to just look at Wii as just that, not compared to the other systems even when they share similar franchises. Wii, and even old Gamecube titles that I missed the first time around, I've been able to come back and play for gaming breaks in the day to just enjoy myself rather then get involved in a big title, and so it's been perfect for me.
Bouncing around in de Blob (ignore the story and just enjoy yourself), World of Goo for a puzzle solving with my luv or a friend, Little King Story for that Pikmin and micro management RTS feel of a single mission for the day, Bit.Trip Runner for that old school "get the stage done, now get it done perfectly", all the light gun games, FIFA 10, and plenty more just fit me as my old Master System and Mega Drive used to.
Still some games to get deep into of course, Cave Story, Metroid Prime Trilogy, Xenoblade, and others to fit specific wants and desires.
Metroid Prime Trilogy is an excellent trilogy of games. It's a first person adventure as some have called it, so it may be hard to get into if you are expecting a Halo or Resistance. It does hold to it one of the best subtle stories you'll come across, as it's all based about you finding the information and putting it together yourself. It's different, but solid gameplay and story.
Super Mario Galaxy 1&2 are two of the best platformers of this generation in my eyes. It's Mario, not much else to say.
Super Paper Mario. I honestly can't recommend this unless you really like a lot of text that will be for humour and platforming. It's funny mind you and there are parts that liken back to the easy and joy of the original Super Mario games, but it goes on longer then it really should.
Super Smash Bros. Brawl. Easy to get into and fun to do with friends. Online can be troublesome at times, but with friends I've never had any real issues. I would also recommend Tatsunoko vs Capcom if you are looking for a fighter, it's just as strong as any vs Capcom title even if you don't recognise the characters.
Wii isn't for everyone, but if you put aside the jokes about the system, ignore the mini-game collections and tie-in shovelwares (which thankfully never got as bad as the PS1 and PS2 had), and keep an open mind. You'll find something entertain yourself with.
