Trailer was amazing. Lots of good stuff was revealed here.
Poke Pelago certainly is my one of my favorite additions made to the game. Glad to see gamefreak resolve a large number of the nuances people had with playing in-game, namely the tediousness / difficulty in EV training, obtaining certain items (namely limited evolutionary stones), and leveling up. The Island that interest me the most out of the Islands they showed is definitely Isle Abean since you can catch wild Pokemon here. This could be this game's replacement for the friend safari and may be the only way to obtain certain Pokemon like Exeggutor in their non-alolan formes.
The 3 starter evolutions look good, through I feel Torrcat is a bit lacking compared to Dartrix and Brionne. Dartrix's design makes it look a lot more talented, yet its general animations make look more snooty, while Brionne's design gives it a more stylish design and its animations makes it seems more energetic and outgoing, perhaps to receive more attention. Torrcat doesn't seem to have much going on in terms of character or design like the other two, though the fiery bell is definitely a nice touch.
Unlike alot of people, I'm pretty glad to see Ash-Greninja in this game and its design looks much better than I had hoped. I feel its new upright stance allows the more unique characteristics of its design, like the frozen Water Shuriken on its back, stand out more, in addition to making it look more menacing. That being said, the demo better give us a good explanation as to why its called Ash Greninja and how it appeared in alola in the first place. Looking forward to using it nonetheless.
Glad to see Mega Evolutions back. Like the new effects the developers used to show the transformation, though I must say that it does make the megas themselves look far less threatening. Being able to buy the stones through an ingame shop is pretty rad too, as I found the quest in obtaining the stones rather tedious in ORAS and XY.