Essentially The gamepad functionality in Rayman Legends is just a less intuitive method of using wii mote as an on screen pointer. When I played the demo, I thought having to look between the 2 screens just to control your fairy friend was a tad exhausting if you're playing on a tv and damaging to the pace of the game (not to say its not enjoyable). Playing the Pupeteer demo with PS move, I was reminded that there have been many games with a similar gameplay mechanic of having a companion to interact with the environment on the wii and they all work better than the gamepad set up IMO (Mario Galaxy, Zack and Wicky and Lost Winds amongst the most notible).
Lost winds, one of the games that used a similar mechanics on the wii.
Would you rather play the game with the wii mote and Numchuck, or with the gamepad?
So far the game is confirmed to support classic control and wii remote play (horizontal), but no word on whether it will support wii mote and numchuck.