The multi-player is only good if you play with people that have moderate/slightly advanced experience with platformers. If not, then it's an absolute blood bath. You'll probably get no where.
Anyhow, the unanimous opinion in this thread is that you haven't played enough of it, which is absolutely true. You can't stop 40 minutes into a 90 minute movie and say you didn't like the whole movie. Many movies start off slower and then really ramp up at the end. Same is true with Super Mario 3D World.
Also, you must have a really horrible speaker system if you think the music is not even just good. Super Mario 3D World's music is a huge step up from the recent Mario games and also almost matches the Galaxy games.