I'm on World 3 currently, and find myself both enjoying the game and disappointed at the same time. For those people saying that this is a return to form a la Super Mario World, I have to disagree. There are a couple of issues that have bugged me about every game in the New Super Mario series, and this game is no different:
1) No indication of which levels have secret exits.
This issue was mentioned on the latest RFN, and Guillaume excused it by saying that Miiverse provides the hints that the level icons are missing. This may be true for NSMBU, but it certainly wasn't true for NSMB or NSMB2 - so to act like Nintendo left that out intentionally because they knew Miiverse would fill that gap is giving them too much credit. I think it just wastes the user's time forcing us to search all levels for secret exits and artificially pad the game length.
2) Yoshi Limitation
This bugs me to no end - having Yoshi leave you at the end of the level is so frustrating. In Super Mario World, you could take Yoshi into every level except for the castles, which in my opinion makes the game feel more varied and enjoyable. Being able to keep Yoshi if you survive throughout the level with him was super rewarding and let you see other levels in new ways.
3) No Flying
This is probably my biggest pet peeve - yes you can sort of float/move upward with the squirrel thing, but it's nowhere near as flexible as the cape that exists in Super Mario World. I think this is just laziness on Nintendo's part, and I felt the same way about Super Mario 3D Land (bringing back the raccoon tail with no flying? give me a break). Being able to fly requires the level designers to accomodate that on every level, and made SMW feel like a larger game that was more enjoyable to explore. I loved taking the cape into levels I had previously played and trying to fly into different corners to see if there were secrets there.
All in all this isn't a bad game, but adding a better world map does NOT automatically bring NSMBU to the level of SMW....at least not in this gamer's eyes. Would love to hear others' thoughts on this...
/rant