So yeah I'm basically finished, haven't gotten all the Star Coins though and obviously those who know what that means know what that means ;)
New Super Mario Bros. Wii may be my favourite Mario title ever, I'm guessing that once I have time to reflect it'll end up being my 2nd favourite behind Super Mario World. I just love the flow of the game, the gameplay, the nostalgia and the new additions and the bossfights are some of the most memorable I've had in a Mario game. Certainly beat any of the 3D Mario titles. I haven't really delved into multiplayer, just a handful of levels, but it does add to the game experience in a very positive manner. 2 Players works the best when you're trying to play co-op but 4 is best for coin battle.
Having completed the game up to the end of world 8 though and I'm a little disappointed in the amount of Yoshi levels. I think they're were only 3 or 4 from memory and that's something that Super Mario World has over New Super Mario Bros. Wii. Another thing is that I died a couple of times by accidentally ground pounding a pit or lava or something but that is a complaint towards the Wii's D-Pad and not the controls of the game, I actually loved the controls and the use of motion really adds to the game. For example shaking the controller mid jump will cause Mario to spin and drift a little bit further than he would have other wise. It feels very natural, just like in Galaxy.
It's a must have game for any Wii owner and could not have been done on any other home console. I say this because the feeling of the NES controller is there only because of the design of the Wii Remote.