A lot of people think its the best Mario game in like 15 years or even ever. I'm a little more hesitant to make any such claims, but it definitely still is quite good. I actually found more fun in a second playthrough trying to get all the secrets and coins, vs playing the main content of the game. Which, to me at least, vindicated my original feeling of the game. That being it wasn't as good as some past games in level design or originality.
That said, like I said before, its still a great game and worth hours of playtime. And still one of the best games on the Wii. Its just got a lot to live up to in terms of Mario games and personally, I had a more fun with Mario Galaxy and even NSMB DS when it first came out.