Just finished my first 100% run, Mario only, no badges except when forced obviously. I probably spent about 15 hours or so on it, taking my time. Stream of consciousness immediate reactions: Overall it was really good, but just a tad short of spectacular. Firstly, it has TONS of personality, something we all were longing for after incredibly sterile NSMB series. It finally felt like a step forward for the series. Some really unique art direction, great animations, and decent music. Controls like a dream, fantastic sound effects, and mostly great level design. Mechanically super solid just to move around through the levels running, jumping, and attacking. Impeccable game feel, so to speak. One level even felt like a Mega Man level to me, it was awesome. The finale (last handful of levels, not the Special world) was super impressive and I was smiling the whole time. I also can't praise the world map enough. I spent a lot of time just combing through the maps looking for secrets. World 4 was my favorite in this regard. I also loved most of the new enemies.
It's crazy how much they took from Donkey Kong Country Returns specifically. The heavy use of foreground/background elements, directly ripping off level designs/mechanics/artstyles seen in Sunset Shores, Bombs Away, and Handy Hazards.
Wonder mechanic is a mixed bag. There was a ton of truly inventive stuff, and at times it really wowed me and added another layer of depth and surprise to the levels. But I felt a lot of the time the ideas they were presenting weren't fleshed out enough. Like here I am on my way to do something that looks really cool, but then it ends as quickly as it began. Also, it can really interrupt the flow of the levels themselves, and there were definitely some repeats that got kinda old after a bit. I do think overall though it was a nice addition to the game, and helped to differentiate it from other games in the series.
I do have some criticisms though. The main levels themselves felt short even though they were in line with the rest of the series. I think this is because a good chunk of the level was often "on rails" due to the setpiece wonder flower moments. This meant that less of the level was made for just running and jumping around as normal. It's not necessarily a bad thing, just not something I really vibed with. Bosses were extremely underwhelming, and I expected a much better effort there. I also can't say I'm the biggest fan of some of the mini activities they had in between main levels. I get that it adds to the variety, but I would have preferred they just made more proper levels. My biggest criticism is the difficulty. Yes, the special world could be challenging, and tons of fun, and I appreciate that. But 90% of the game just doesn't push back hard enough. Most of the ideas presented weren't pushed quite as far as I would have liked them. This was a far easier game than the NSMB games, and to me that's a bummer. The final level was indeed a doozie though. Not quite Champions Road, but it kicked my ass pretty hard and it felt great. I started it with around 40 lives and beat it with 1 life remaining haha.
All that said, this is definitely one of the better 2D Mario games methinks. I'm not sure if I'd rank it third or fourth. 3 is first, World is second. I'm tempted to put Wonder 3rd, but NSMB Wii, despite following it's bland template, is just such a masterclass in level design, and provided a satisfying challenge. I'll just say their tied haha. Now if only we can get a proper 2D Zelda!