I think the main game is great but the post game became such a repetitive grind. Was already tired of the races after the first one.
The koopa races became boring very quickly. I always put off doing them until the very end. I was ok with them in SM64 and SMS (against Pantisimo?) because they brought variety to the games, but in Odyssey they're in pretty much every kingdom.
I didn't think it was that much of a repetitive grind other than that though.