I've been playing Mario games for most of my life, so I was beyond ecstatic when I got to play this game! Super Mario Bros. 3 and Super Mario World are my favorite games of all time, so I have a special spot in my heart for 2D Mario, but definitely felt like the "New" Super Mario Bros. series was getting a bit stale. Super Mario Bros. Wonder is a much-needed refresher from that, and the new Wonder Flower mechanic makes for an experience with almost no dull moments. At times it felt like I was playing a modern re-imagining of Super Mario World! It's classic Mario platforming at just about its finest, with plenty of new ideas thrown at you by the minute. This is probably the most creative Mario game I've played besides Super Mario Odyssey and Galaxy 1 & 2! Badges and new power-ups are great additions as well. Elephant Mario is such a weird idea but I love it for that! The art style is really cool as well: it's cartoony but so much more expressive than the "New" series. The locales also take traditional Mario tropes and put fun spins on them.
The only real problems I have with the game are minor. I do wish there were more bosses than just Bowser Jr. and that they were more creative, especially when the game is already brimming with creativity. I wish there were more boss fights in general (two worlds don't even have an end boss!) Some of the Wonder effects do feel a bit disconnected from the regular gameplay, and as a result, some of that classic Mario platforming goodness, pacing, and thought-out level design is sacrificed in favor of a mostly visual spectacle. Those instances are few and far between though. An argument can be made that the abundance of different Wonder effects gives the game less of an identity, which I can definitely see. The difficulty is on the easier side, which makes for a pretty quick 100% playthrough for Mario veterans, but still offers some good challenges in the Special World.
Overall, the problems I had didn't really impact my enjoyment of the game that much. I'd give the game 4.5 stars if Google let me, but I don't think it just deserves a 4 (hence the 5 star rating). Without a doubt, this is the best 2D Mario since the original New Super Mario Bros. on the DS. It almost reaches the pedigree of SMB3 and SMW, but just has a few things holding it back. I love the game though, and I think a potential sequel that addresses its issues could easily be the best 2D Mario ever made.