Personally, I think more third party games would be good just so we can have more variety. The only good Nintendo games for the Wii are Brawl and Mario Kart (don't kill me, fanboys), and I'd prefer more things like MoH: Heroes 2...

However, the Wii will likely be starved for third party games because the Wii wasn't made for things like CoD4 (although if they made a game that did a better job with the motion sensor than Heroes 2, it'd sell like crazy), and it's games like CoD4 that sell. It seems that Nintendo targeted a younger/casual gaming audience with the Wii, and there's less money there for developers.

I personally liked Oblivion, and think it would be good for an FPS fan. It's got its flaws, but the combat is nicely done, and the story is interesting enough to keep you playing. It suffers from a short storyline, but your average FPS player won't care too much about that really.

Final word, I'd say go for it. It's definitely worth the investment.

Morrowind or Oblivion would be my opinion. You could get them on consoles, true, but I liked the PC version of Morrowind better, at least.