Went through world 8 today.  Some good stuff in there.  I think 8-7 with the dinobone coasters is my favorite level in the game.  Was really neat.  I like how the boss fights in the last few worlds really tried to change things up.  World 7-8 were kinda hard going for 100% completion.  I got to world 7 with 65 lives and finished the game with 35  :'(  While I love that the game was actually challenging, it's a love/hate thing because it's been a while since I've played a game that makes me want to throw my wiimote in frustration over and over.  I hated 7-6 with the flying beetles.  Oh god did I hate that.  Also any level with wii gimmicks, definitely hated those.  Not sure if I want to try world 9 today as I think I've had my cup of tea of dying for today.
I think while NSMB Wii has been a great, great game.  I enjoyed it less than the other marios because in those games I wasn't worrying about finding all the big gold coins and wasn't jumping into every wall and searching every cliff for them.  I was just running through the levels enjoying them.  Going 1 level at a time here getting all 3 coins before moving to the next, the game was a mix of fun (discovering the coins!) and frustration (dying and redoing the section over and over until you have them all in one go!).  I think I like Mario better when you are just focusing on what's in front of you to get to the end of the level.  I could have just not gotten all the coins, but I have collectathon ADD in games and if there are things to collect I feel like I must 100% them all.
Will try world 9 tomorrow.