Bought the game. Put about 15 hours into it so I think I have enough time with the game to make a review.
Bottom Line Up Front: Typical paradox release. A technically complete game, it lacks the depth that will undoubtedly be brought about by DLC (as is their pattern). I'd give it a 7/10 right now. Anticipate 8.5 when all the DLC gets released.
Don't feel like writing a full review, so I'll just give three positives and three negatives
+Interface. Game looks great and handles the information on the screen nicely.
+Options for game creation. Whether this be designing your own race, how the galaxy size is and looks, etc. A nice touch is that you can designate a certain amount of races to have a "head start" which makes it more realistic (not like the entire galaxy discovers space travel on the same day). So you can bump into a huge empire right in the beginning.
+Technology. There is a lot of it, and I like the semi-random nature it is presented to you. You are given a choice of technologies to research per category (starts at 3, but can be more as the game progresses). You choose one to research. The ones you don't choose get shuffled back in, and you don't know when (or if) they will reappear. These aren't completely random, as certain tech is needed before future tech (you wont' get anti-matter drive, for instance, as an initial choice).
-The AI. It is pretty atrocious to be honest. In the beginning I didn't have much resources for fleets so I just had one sizeable one. While this fleet was on the edge of my empire, I got invaded by an enemy. I fought them and got wiped out. They continued with their fleet to Earth. I was trying to manufacture/scrap together a new fleet, but figured I was toast and was going to have to restart the game due to me miscalculating and not building up my defenses. Instead, the fleet just bombed earth for a few days then randomly just traveled in a big circle around my empire, not attacking anything. I eventually built up a fleet and destroyed theirs, then conquered their empire.
Another example, and this is something that happens every time, is allied fleets. Whenever you get into a war and have allies, the allies send their fleet to assist your fleet. This sounds all well and good until you realize they will send their fleets to assist yours WHEREVER YOURS IS. One of my allies got attacked by an enemy empire. My fleet was dealing with some minor aliens on the opposite side. I figured my ally could defend itself while I cleaned up the aliens so I could continue surveying that system, and then I'd move my fleet to help them. They sent the ENTIRETY of their fleet to "help" me mop up the alien ships and left their home worlds defenseless to the enemy advance (though not that it really mattered as, like I said before, the enemy attacking AI is pretty bad). This happens every time you get into a conflict. I am part of a federation now (A federation is the next step up from an alliance and needs at least 4 participants... I've named mine "The United Federation of Planets" ) with 6 races, and whenever we go to war I get like 10 fleets following my main fleet, wherever it is (chilling at my home world, repairing at a station, going off exploring...). Hugely annoying.
-Diplomacy. Well after writing the above I'm a little exhausted so I'll just say the diplomacy is pretty shallow. Not up to what I'm used to with CK2 or EU4, though I expect this to get expanded with DLC.
-Combat. Combat is pretty bland and uninvolved, though I'm not sure how they could improve it with the model they have.
Final Thoughts/Recommendation: Good enough to scratch that space empire itch, but I'd wait until at least a few DLC's are released.
*I will note that I've experienced zero bug related issues (slow downs/crashes/glitches/etc.), so for me it is really polished in that regard.