I played it for 6 hours last night, loving it so far.
The aliens are pretty difficulty in the early game, which is better than Civ 5 barbarians I think, but after a few unit upgrades they are dead pretty quickly. The Kracken though, that's something you don't want to mess with, it kills boats in one hit. I've lost 5 Gun Boats so far.
The tech web and affinity system is really good, it will make players have different units at end game, rather than everyone having the same like in previous games. I've gone for fast Supremacy progression, and now I can kill AI players like they are nothing because of the unit upgrades. I think maybe some of the upgrades are overpowered, but maybe I should play on a higher difficulty. The CNDR just eliminates everything I can find.
Something that needs to be added is trade route automation, each city can have a certain amount of routes, and towards the end of the game you're going to be choosing where to send them every turn. There needs to be a button to automatically go back to the same place every time. But other than that, I haven't found much that I don't like yet.