I took some time to think on it after finishing season 2 last night, and while I'm not going to give away any spoilers...I found it very disappointing. The most I'll say is that one of the main perks the second season promised us - an exploration of Niko's backstory - is only brought up abruptly in the last half of the last episode. And while it is an interesting concept, it needed more time devoted to it both in-universe and out in order to truly flourish, and the execution of it is very rushed and sloppy and leads to the previously-mentioned ending of disappointment. (Without giving too much away, it's similar to how The Legend of Korra's second season ended off, in more ways than one.)
And while that is unfortunate, it's easier to stomach when season 2 already didn't raise my expectations higher than the first season already had, and since that one already ended on a perfect note, I'd say. The animation saw a marked improvement with many awe-inspiring effects, and some of the new settings were appealing, but the new characters weren't memorable (and never came back like the ones from the first season did), and the interactions between the original team started to get slightly stale after a while. Niko and Lyra reached their peak at the end of the first season, so their interactions here usually amount to sibling-like banter and such, Mandok is his usual cowardly self...and the one other thing I didn't like is that after growing into such an impressive shape by the end of the first season, Flicker starts off the second by regressing back to his base form, and he stays like that until the series ends. It was like they felt the need to shrink him down to make things more challenging for the heroes, but why not just leave him in Carondolet to begin with?
The second season also ends with hints that there may be a third sometime in the future, but it's worded a little vaguely, and honestly, even if it were true, the way the characters end off this season (one of them, specifically - again, no spoilers) makes it seem unlikely that I'd feel the same endearment toward them if I were to experience the story's continuance. Once you've seen for yourself the past few episodes, hopefully you'll comprehend what I mean.