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)

Nice to hear!

I have the strategy guide, and it states that the dialogue is different, and the dungeons are as well, in subtle ways. Is this true?

Also, glad you like it!

There are a couple of instances when people tell you that you are playing in Hero Mode. Like that guy who tells you to focus on him with the Z button in the beginning of the game. I skipped all cutscenes, but I don't think that they've changed one bit.

I didn't notice any differences in the dungeons, they are exactly the same.

In response to your previous post, text doesn't scroll faster than usual. Just like before, you can only speed it up a little bit by holding down the A button. It's possible to override the fourth point on your list with a certain item. The game even tells you as much.

I haven't noticed different dialogue apart from me choosing different options to answer questions. As for dungeon differences, only done the first one so far, didn't really notice much difference apart from the lack of hearts, I think some of the treasures (amber relic etc) may have moved.

I'll try and take more notice in the 2nd dungeon.

There are a couple of instances when people tell you that you are playing in Hero Mode. Like that guy who tells you to focus on him with the Z button in the beginning of the game. I skipped all cutscenes, but I don't think that they've changed one bit.

I didn't notice any differences in the dungeons, they are exactly the same.

In response to your previous post, text doesn't scroll faster than usual. Just like before, you can only speed it up a little bit by holding down the A button. It's possible to override the fourth point on your list with a certain item. The game even tells you as much.

It's better than The Wind Waker, but worse than Twilight Princess. For now.

It doesn't come close to Majora's Mask, A Link to the Past or the original game. I am a bit disappointed.

All the filler gameplay and there was quite a lot of it, especially towards the end. The developers should have put more emphasis on the combat and used that to make the game longer. You can't even upgrade your sword which is the most important aspect of an upgrade system. It's all about growing stronger, but SS fails on that level.