There's something wrong about it being a requirement to collect a certain amount of electoons in order to play more of the game. Yoshi's Island was an exploration based platformer, but at least you didn't have to get 100% on all levels to go through the main game. The only thing you'd miss out on were the secret levels. I don't really like the concept of unlockables, and being forced to unlock the rest of the game makes me not want to play.
Visually? The game is very nice to look at, but I've seen better looking platformers before.
I don't think the game is as polished as you say it is. The controls could be better for one - crazy as that sounds. Sometimes I bounce off of a wall automatically when I perch on it after using the helicopter. Don't know why it does this, but it's very annoying. The run-up-wall mechanic is also very misleading, I forgot why, but I think it's cause you'll keep running even after you let go of the directional pad. Also, sometimes you get combo-juggled, which is annoying when you have an extra hit. It's essentially an instant death.
The swimming is leagues better than most Mario games to say the least, but I can't help but feel it could be better.
Also, the water levels were very underwhelming - not much is done with them, and there is a lot of unused space that's just sorta there.
Also, just wait until the later levels. You are forced to rush or else you will die.
I can't really say I agree the level design is great either. It's unengaging. unlike Mario, where enemies are well-placed, in this game, there are barely any enemies worth mentioning. They are all extremely easy to get rid of. I don't really feel like I'm ever in danger except in the areas where you are forced to rush, and you can rush through pretty much any stage within a few minutes. Pretty much everything in this game has been done better in some other platformer, like Yoshi's Island.
Which brings me to another point actually. Most of the levels in this game are unmemorable. Unlike Mario, where each level had a theme that it focused heavily on, Rayman Origins doesn't do such. The game focuses mainly on acrobatics, and designing levels where you use these in creative ways rather than making each level feel different.