The best platformer game ever created was missed by many or at least misjudged and passed over due to the Wii U's failure. Super Mario 3D World.
I can't remember a time that I played a game through that continuously gave me this much joy and then added surprise after surprise with more and more content and challenges. I want to note that I played this game BEFORE & AFTER Odyssey. In fact, I beat Odyssey (with 900 moons). I have been recently playing both games with my 4 years old daughter.
Anyways here are my reasons:
The game still looks absolutely stunning. It has a way better image quality than Mario Odyssey. Smooth framerate at 60fps with not a single blurry texture. Very colorful.
Incredible level design and difficulty balance which gets progressively harder at almost the perfect level. Mario Odyssey is just too easy. It just feels like roaming around and getting moons (90% are very easy) and it gives no sense of completion or challenge to me like Galaxy and 3D World. And level after level, they always introduce new mechanics or new elements to each stage.
Ongoing content that just keeps going, opening up surprise worlds that feel fresh, fun and really add tons of value. Unlike Odyssey where the main game feels like 4-5 hours long...This game continues and feels fresh all the way until the final Bowser fight...then keeps going and going with surprises.
Real innovation that integrates amazingly creative new game elements, like the Toad levels, stamp collection, getting the "top" of the flag on all levels. These all feel like real challenges and you actually want to collect EVERYTHING. (Edit: I'm not saying getting the top of the flag is a "challenge", but it's something that's inherently "Mario". It's cool that they turned it into an objective in each level rather than just extra points.)
You can play this game in single player only and you'd almost forget that you can also play multiplayer. Some may disagree, but I'm willing to bet you jumped right into this thinking it's a multiplayer game and didn't really give single player a chance on its own. Playing in multiplayer makes it feel like a totally different game. It's like two games in one. Try it single player only and beat it that way, then go back with multiplayer. You'll see what I mean.
Integrates all of the best "true" Mario elements into one. Maps opening up worlds like Super Mario World (SNES), playable characters with different attributes like Super Mario Bros 2 (NES), random roaming enemy challenges on the way like Super Mario Bros 3 (NES), all with a very Super Mario Galaxy feel and amazing creativity.
Great audio tracks. Odyssey has loads of forgettable music, while this game gets stuck in your head. My girlfriend and I literally had many of the background tunes in our heads daily after playing this. Love the "circus" Bowser level music.
The cat suit is really fun and a welcome addition (the Tanooki suit is the only forgettable one) and makes finding all stars fun. However, the real creativity is in the bullet block head, light block head (later boo levels), coin block head and more (like NSMB but I think executed very well here). Seriously, there is amazing creativity here in using so many game elements to add value to already great level design, I don't even know where to start. It's like the Mario Galaxy team brought all their best ideas together and put them into one game. There are time rush levels, speed levels...it's the perfect amount of pacing and change to keep it interesting all the time. Odyssey has less of that innovation and feels the same the whole way through, except for maybe changing and collecting outfits, planting seeds, some races and a few others.
Perfect integration of real classic Mario enemies. They're all here, from spiky turtles, to mini Goombas. What really stands out though are the little touches. Like Goombas relaxing and sunbathing in tropical levels. Look for the little touches that make this world come alive. It's so much fun because it makes you smile all the time.
I could go on and on, but I just wanted to get this out there. I still think Odyssey is a good game , but I prefer the map style of Galaxy and 3D World where I get a sense of accomplishment from beating a level and then moving to a different one rather than roaming through one massive area with WAY too easy moons. Odyssey for me is the least "Mario" title so far and while that may be refreshing for some, I think it was highly overrated because many people skipped the Wii U and hadn't had their Mario fix for a long time. It made people get too excited and more reviewers were "wearing rose colored glasses" as the saying goes when they played it. Honestly, I implore you. Go find a cheap used Wii U and play Super Mario 3D World. Don't miss the best Mario game ever made. Note: Galaxy 2 is extremely close for a score for me. They're almost neck and neck...but I'd give 3D World the slight edge.