I have played something like 6 hours, and I have a good feeling mixed with some (worries.
I liked the beginning, with all the events, exploration and a menace of being boxed in as a whormhole power between my ally and my rival. I had some problems with the UI, especially with how planetary capitals are supposed to be upgraded, and I guess I was a bit too reckless with my fleets. Still, I managed and I won my first war. I guess I took too much, but I easily prevented a rebellion, not without almost runnimg out of energy, thought (which could have been prevented if I had know how to upgrade planets properly).
I like the Ship Designer, which is something new for me in a Paradox game, but I'm a bit at a loss about the optimal build. There should be some quick indication on what I'm changing on my ship by adding removing components. Other than that, I liked being able to have a second wave of exploration, but I have the feeling that after I colonized a Gaia world and definitely crushed my rival, the AI, which wasn't so awesome in my last war against my rival, won't be a match anymore (except fallen empires). It may be too soon to say that, thought.
Ho, also, I didn't manage to uplift pre-sentients in an habitable world in my empire. Somebody has a clue how to do that? (nevermind, I need a special tech...)