Hadrian, have you ever played the original Rayman? It's very hard actually. But half the challenge isn't beating most of the game, that's manageable. The hard part is going into the stages to find ALL of the cages to free the 'toons. You can't beat the final boss or see the ending without them all collected.
And they made the game easier on the GBA. They gave you more lives, put in more platforms in hard jumps, made the bosses easy to exploit (you could hit some of them all at once without them fighting back), and they removed several of the auto-scrolling screen parts (where you used to die if the screen catches up to you). The original PC, PS1, Saturn, and all other versions were much harder. On the other hand though, you have less of a view in the game, due to much smaller screen resolution.
And I've not had much trouble with some of the Treasure games. That's just me, but I found Rayman 1 considerably harder. That being said, I have beaten both the original DOS game and the GBA version without using cheats or anything. That is completely beaten.