I played a friend's copy of this game today, and holy fuck this game is good. It really took me by surprise how entertaining this game is, and there's just so many laughs to be had playing this game in coop. I don't even generally like Mario games as much as most people, I mean, I consider them to be good to pretty good games (I especially liked Mario 64), but in general I don't hold them in as high a regard as many gamers. With that being said, this game feels like it could be a GOTY contender after I finish it as well as the rest of the best games from this year that I haven't played/finished yet.
My brother and his wife are getting here tonight to visit for about a week or so, and I'm really tempted to go out and get a copy and a second Pro controller so we can all play coop.
It really seems like a missed opportunity with the lack of online though. I feel like this game could have been huge if they included it. I know personally I tend to shy away from games with coop if I don't have anybody else to play with since I generally consider coop to be the most entertaining way to play games when it's available, and online would help so much with enabling more people to play coop whenever they want. I really hope they'll make a sequel and include online.