A christmas gift from our friends, I received SMG and didn't really get to sit down and enjoy playing it until about a week after.
And everything you've read about it is true. It really is that good.
There are a couple caveats, though. There's still that insane voice acting on the part of Mario, almost no voice acting on anyone else's part, and the game can be a little trippy. Running and jumping upside down, for example, detracted the wife from enjoying it as much as she does playing Mario 3.
But other then that, its flaws are few and its qualities are many. The best part is, of course, playing the game with friends. But I only got to do that once - although an absolute blast it was. Plus, Mario in a bee suit! Fun stuff.