I've only completed World 1 so far. Here are my initial observations:
-The gameplay hews very closely to the DS version, so those who weren't fans of its throwback to simpler, slippier, more rigid controls probably aren't going to be any more convinced here. In fact, the game somehow feels slightly more rigid than even NSMB DS was. At the least, the timing was tweaked just enough that I was killed by the very first Goomba on the first level. (Yes, I am thoroughly ashamed, because as I was approaching it, I was saying to myself, "Please god, don't let me run into him." And then, WHAM!)
-Some other gameplay tweaks appear to have been put into place. Performing the triple jump, for example, is slightly harder to pull off in that it feels like you have to take a longer sprint. Another example is that ground pounds will take a regular Koopa completely out of commission, unlike the DS game where they would shoot across upon impact. Still another example is that you actually need to continue holding DOWN when performing the downward screw drop from a springboard jump or Propeller Suit boost. In the DS version, simply pressing down once would keep you in the attack formation until you automatically touched ground again.
-The sporadic use of Wiimote waggle is brilliant at times, irking at others. For instance, using it for tilt platforms is pretty neat, in that you've got a "pat your head, rub your tummy" kind of mechanic happening: keeping your horizontal Wiimote in position while executing the appropriate leap is an innovative touch. But then you also need to waggle whenever you want to leap off of Yoshi, and more than once did I find myself accidentally dismounting because of unintentional movement of the 'mote. Same goes when using the Propeller Suit, where I accidentally launched myself up into the air at a rather inopportune time.
-Yoshi's a bit of a weird beast here. A hodgepodge of Super Mario World and Yoshi's Island, he retains his temporary midair float, but he can't do a vertical tongue slurp -- but nor can he do a slightly elevated standing one, like in SMW. No ground pound when you're on him either, and unlike SMW, he can't slurp enemies through solid objects like pipes. There are different colored Yoshis, but like Yoshi's Island, there's no difference between them gameplay wise. (In other words, no special abilities like unlimited flight or fireball spewing from SMW.) You do spew fire from eating a Piranha Plant, though, as opposed to a simple spit-out before downing a Koopa. Along with being able to do a leaping dismount, I can see some cool midair gameplay possibilities when using Yoshi in conjunction with the Propeller Suit. Oh, and the stage music changes up with a layered percussion, just like SMW.
The exclusion of the reserve item box a la World and DS NSMB is missed, but in its place is the item inventory system from SMB3, where you can accumulate and then choose a single item to use before starting a level. I'm going to guess this will come in handy later on when you need to use specific items to nab Star Coins. Oh, and I love the new streamlined look of the inventory; no longer is it a clusterf*** of everything you've collected. Now it's Mushroom x5, Fire Flower x3, Propeller Suit x1, etc.
-The overall structure of the game feels very SMB3. The random enemy encounters on the map, the mid-level Fortress, the Airship, the robust number of Item Houses and bonus chances to earn extra lives, the inventory screen, and the presence of the Koopa kids..... They all add up to a very compelling bit of nostalgia.
-Lives are still very much in plentiful supply. Without trying too hard, I managed to accumulate a healthy total of 23 lives by the end of World 1. The levels definitely feel longer and more substantial though, moreso than in NSMB DS. There are trickier enemy and platform placement, more hidden nooks and crannies to explore, and there have been a number of levels where you need to think out a solution to grab those Star Coins. Imagine my surprise when I found myself running out of clocked time on a daily basis.
-The Save System is well implemented here. Quick Save as a one-time suspend save and load session, permanent save after beating a mid-level Fortress or Castle. It's to my understanding that completing the game will allow you to save at any time, just like DS NSMB.
-Am I the only one annoyed by the game's insistence of showing you the same obnoxious hint box each and every time you earn an Item for inventory or come out of Peach's Castle to view the Super Skills/Hints section? Mention it the first time, fine, but EACH AND EVERY TIME? I'm hoping they'll cease once World 2 begins.