Let me preface this by saying I loooved Galaxy (I 242 starred it, or whatever the max was), and like most guys our age, 120 starred World a couple times when I was a kid.
I think Odyssey is great - but it's not better than World or Galaxy (so far).
Upsides:
This is the Adult Swim of Mario games. So many random elements and possessions guarantee you have not seen anything like this.
The music is fantastic - even better than Galaxy's orchestral sound track.
Plus the standard great gameplay.
Downsides: This is far less directed than Galaxy. To be clear, anyone who hasn't suffered recent head trauma can get enough moons to open up the next world. (Apparently the game is structured a lot like 3D Land, so you are actively hurting yourself by trying to clear out a world prior to "beating" the game.) But when it comes to getting all the moons, its like pulling teeth - you can get the "name" of the moon and pay 50 coins to get the location on the map, but that doesn't help much when it just shows the entrance to a sub-area. Stuff is hidden everywhere, and its not always clear if you can't get something because you haven't hit the first ending or because you didn't try something.
Controls seem a bit wonky - way too easy to overcorrect and have Mario do his backflip instead of jumping forward. Also seems tough to walk in a straight line, but that may just be me not being used to the Switch controls (only bought it last week and have only played Picross.
Motion controls are essentially mandatory (in spots). There's a non-motion option for one or two moves (although the option is annoying itself), but it's been proven some things cannot be reached without a longer motion-boosted jump. The flicking isn't really easy even on a pro-controller - so (at least a couple spots) are essentially JoyCon Mandatory.
Quasi-spoiler: The reward for all moons is another 3D Land-style death course. Unless you are collecting things for the fun of collecting or have 12 year old reflexes, it's not worth it.
If you have the limited spending power and infinite free time of a preteen/teen, this is probably the best Mario ever. For everyone else, it's merely one of the best.