I wish I could have got into it more. I played Galaxy 1 and 2 around the time I got it, and rather than getting me in the mood for Mario Odyssey, they actually served to make me feel a little underwhelmed. The experience isn’t as grand, varied, or as interesting as the Galaxy games IMO; the level design is a step down from the Galaxy games. Another issue is the size of the game, it is smaller and shorter than the Galaxy titles; difficulty is substantially less; a big and it is not nearly as rewarding. It’s closest to Mario Galaxy in how it feels but, despite the new features, still comes off as a reduced experience; like the Mario team is still holding back.
In terms of sales, those numbers are off. Nintendo says Galaxy is the highest selling 3D Mario game. Odyssey is the fastest, though. This is a trend we’ve been seeing in multiple franchises on Switch.
Yeah the Galaxy games were very good. I remember thinking Galaxy was amazing and then Galaxy 2 was even a bit better, even though the wow factor was gone since it was the same experience just better than Galaxy. I don't think Odyssey is necessarily better than the Galaxy games, but it does go back to the Mario 64 style gameplay with big platformer worlds. Whether that is better or worse than tons of tiny planets is up to each person to decide.
Mario Odyssey is a big game though. I'm 55 hours in and still trying to get the last bits done (granted I beat the game I think after about 25 hours). And the cappy mechanic is the coolest gameplay mechanic that's been added to Mario since Yoshi 27 years earlier. Cappy adds platformer elements and lets you control enemies which adds a whole new level of play. When I first saw the video that showed you can take over enemies with Cappy I was blown away and right then I got very excited about getting Mario. Odyssey is a large, gorgeous, incredibly well made Mario that introduces awesome new gameplay mechanics, has a ton to come back to after you beat the game with awesome diverse interesting worlds. I often feel that Nintendo games are a bit too easy, and that continues with Odyssey, but that would be my only gripe in an otherwise phenomenal game. It may or may not be better than the galaxy games, but it is no surprise that it is killing it in sales.