I kinda wished they'd touched on a couple of faults that happened during Vol. 2.
The repetitive nature of Maya and Alejando's storyline, and the illogical - and somewhat rushed - setup of Peter in Ireland. These were the biggest problems I had with the show, but any other niggling issues have been answered or acknowledged by Kring, or just minor for me not to remember what they are!
Oh yeah... Nathan. I felt, while I was watching him (haven't seen the last two for they've not aired in Australian yet), did not have much to do by way of characterisation except to search for his brother and revel in guilt over the Season 1 finale events, compared to brisk development in about the same amount of episodes in Vol 1. But that was something I had notice, and it would have been deliberate anyway: his arc was broader, and he basically relied on other characters to get to certain signposts that would advance or belie deeper character development.