Here's some info about the second quest:
- Cut-scenes are skippable.
- Text is still not skippable 
though I think it might be scrolling faster (maybe it's my imagination)
- Double damage from everything (falling/enemies/lava etc)
- There are no hearts to collect when you get hurt! (ie no heart flowers, cutting grass or smashing pots won't give you hearts) the only ways to get your health back up if you lose some is by finding a heart piece, using potions or fairies or if you find a seat or bed to relax on (obviously beds are skyloft only, seats can be found on the ground but I don't think there are any in the dungeons) [oh, not tried drawing a heart on the magic walls yet, they may give them out]
- You keep your bugs and treasures that you had at the end of the first quest, which is useful because you will need to upgrade quicker and actually use some potions (I didn't really need potions much till the end, I have probalby used more in the second playthrough than I did in the first, even though I am only just past the first dungeon)
