El Dango said:
3. The fact that this level actually almost has its own plot.
So do Pink Plant Woods(because he meets Betilla),
Anguish Lagoon(the fight against Moskito and the way they become friends, and he meets Betilla again),
Allegro Presto(because he meets Betilla and Mr Sax),
Mr Stone's Peaks(he frees the Musician's guitar, flies through a spiky cavern, and gives some ropes a haircut XD before fighting Mr Stone and meets Betilla),
Space Mama's Crater(because Mr Dark kidnaps Betilla),
Eat at Joes(because Joe gives Rayman a firefly so he can get to the plug and plug in Joe's lights),
Mr Skops's Stalactites(because Betilla cries out for him to help),
Mr Dark's Dare(which has so much stuff going on that I won't even mention it)...
...now that I think about it, it seems that R1 actually has a plot itself!