I really enjoyed this game. One thing no one really mentions is how vertical many of the levels are. Mario isn't necessarily moving to a location far away on the map, or jumping over gaps, but instead the platforming is heavily focused on climbing up the level. The FLUDD emphasizes this, and I thought it was an interesting take on the traditional Mario style. There was a lot of creativity in the game: new enemies, places never before seen in a Mario game, interesting puzzles and boss battles etc. While it's not the best Mario game, it's still damn good.
HOWEVER, I can understand why people hate it. Many levels had a nautical theme, and while they were pulled off in different ways, I'm sure a lot of people got tired of seeing water. It was also easy to abuse FLUDD, so timing jumps wasn't really an issue since if you messed up you could just give yourself a boost. That's why so many people loved the FLUDDless levels, because it forced you to go back to your Mario roots and it was harder than it should have been since gamers were now accustomed to having FLUDD help them. Also, the final boss battle was literally against Bowser taking a bath.