OK, I bought this a few weeks ago on a steam sale (like 20US$ for those who wander) and I say this is an incredible game.
I played origins on the Wii and loved it, although I didn't care for the mosquito levels; but this game is better in every single way to Origins (Wii version was superb btw, HD or not; don't touch the 3DS version though).
I love how the levels are larger; Origins had levels separated by doors, so there were many "rooms" in a level. Origins still has some rooms in some levels, but there are much less and it feels better IMO.
Gone are the mosquito levels (I'm in world 4, so I hope I'm right) and the non Rayman stuff, and that's awesome.
I'm playing on PC, so Murphy levels don't control very well; but it's really a non issue; I even got gold cup in the Murphy challenge; maybe it's easier with a button press than WiiU.
I love the challenges; it's awesome to measure your skills against others, and the climbing, distance and some speed levels are very fun. Killing enemy challenges or getting lums suck though.
The game has some Origins levels too, in a special section, and when you play those you'll notice that those levels were much worse than the new ones in Legends.
There are special music levels; where the gameplay is synchronized with music and are really fun, shows you how much love the developers put on these.
Buy Legends (it will be bomba priced very soon); it's an awesome game, much better than Origins; still not on par with DKCR, but still is very good and there are some levels that are absolutely insane. And cuts all the filler crap Origins had.
Only bad point is that there is no tutorial, so you have to remember all the moves from origins (I had forgotten that the jump when running up a wall was different and felt hell in a distance challenge, until I figured it out).
Also, what's with the soccer game? it's only playable online?