I only played it for an hour or so (so we couldn't unlock all events yet), but here's my impressions. Partially I agree with Shams, partially I don't.
Controls / Gameplay:
Mostly great. You need some practice, though - don't expect to win every event the first time you try. But that's a good thing, I think.
- All Running events are a bit simple, of course. But fun.
- Long Jump / Triple Jump feels good, and you need skill.
- Javelin Throw feels very natural, great.
- Trampoline is hectic and funny.
- Swimming is all about consistent timing, not frantic waggling. Cool once you get it.
- Table Tennis is better than Wii Sports Tennis. Seems like you can get really good if you practice a lot.
- The rest I don't remember right now... but I know that I hated Skeet Shooting. The targets are tiny and much too fast. But then, I absolutely suck at FPS's, so...
Graphics are good, but not great, and the music is a bit generic (unlike the impressive title theme). Menus are a bit awkward and not quite as idiot-proof as in an original Nintendo game. So I'd disagree with Shams about the "overall level of polish" - it's not quite up to first party standards.
But the Gameplay was really convincing, which to me is the essential part anyway.
So I'd say 80something. I like it better than Wii Sports, overall. It's not quite as balanced and accessible, but deeper and more substantial.
Annoying: In Germany it's 60€ - one of the most expensive games for the Wii (SMG is 45€, for reference).
Edit: It's cheaper now on Amazon (49€).
Currently playing: NSMB (Wii)