So, I've just completed the main story, and I want to share some of my impressions.
The best part about SCO by far was its "middle part" – the one where you try to convince various alien races to join your cause. That part was extremely action-packed, and I never ran out of things to do. Well done.
However, the problem is that this part didn't last too long – and after the first boss battle against a Scryve Juggernaut the story became completely linear again. And the final part of the game had a really low point where you have to fight your way through swarms of Scryve ships to get to one of their bases. While it didn't feel as hopeless as getting trapped in the Ur-Quan space in SC2, it still was extremely tedious.
The quality of the story and the characterization in SCO varies a lot. The early part of the game is just too silly. While SC2 had a lot of silliness, SCO really goes overboard with it, early on at least – you really begin to wonder whether there is going to be a deep story behind all those jokes. The story does get more serious and more detailed later on, but like I said before, it doesn't last. My favorite race in SCO were the Pinthi, while my least favorite were the Xraki, who really are as one-dimensional as a character can possibly get.
Finally, why are there so few dialogue choices for the player? For a game whose selling point is nonlinearity, most of the conversations have less choice than in Mass Effect. This is just disappointing.
So now... I don't know what to make of it. I really expected this game to be at least twice as long as it turned out to be, and expected more challenging puzzles and dilemmas from it.