I feel it has the foundation to be a good game but they missed a lot along the way. Certain minor annoyances pile up to make mid-late game, and even early game at times, a chore rather than fun. The warscore system, for example, doesn't translate well from EU into space, as many have mentioned before - why stop at only a few planets every 10 years? Why is there no auto-explore option in the mid-late game, where you can potentially have tens or hundreds of systems within your reach to survey? Why is there no way to survey all the debris in a system in one go (I know they're adding that in 1.2, just amazing that they hadn't in the initial release).
The utter lack of impactful late game technology, at least to me, is also a huge downer. Coming off games like Star Ruler and Galactic Civilizations, where you can get things that destroy planets and solar systems or create new ones, getting minor 5-10% bonuses stretching to infinity makes technology just about getting slightly better guns (aka particle/tachyon lances) and spamming as many ships as possible until the hard locked 1000 fleet cap.
Not to say I haven't thoroughly enjoyed myself, and further enjoyed tinkering with mods and making some basic ones of my own, but it's got a long way to go until "vanilla" is a worthy game on its own right.