It turns out my fears about this game were mostly unfounded. The UI is, indeed, horrible (having to confirm the end of my turn every damned time is a needless pain in the ass), but aside from being in 2D, it's a lot like Space Empires V, a game I previously enjoyed.
My biggest complaint about the game is that your rival factions do not respect borders. They will send massive warfleets through your occupied systems without any warning. They even sent colony ships to my main system to settle on the tiny, basically worthless planets I was saving for a time when I ran out of room to expand. If there is anything more infuriating in 4X games than forward settling, I have yet to experience it.
But the real problem is that I, as a player, am ill-equipped to deal with it. "Those settlers have set up camp with the obvious intent of making my borders unviable, but they haven't actually attacked me yet" is one of those things where my peaceful instincts conflict with my rational strategic assessment. It's something that is only exacerbated by my military unpreparedness. I'm experienced enough with the genre that I really should know better by now - you should always be prepared to wage total war with your strongest opponent at any moment. I just find the entire exercise of strategic warfare to be uninteresting.
I think I just have to accept that aggressive xenophobia is the way the world in Space Empires IV, start a new game where I plan on having powerful fleets from the very beginning, and hope that I don't get too bogged down in slugging it out with aliens with a poor sense of boundaries.
It's making me furious just thinking about it.