I'd also put the UI forward as the biggest problem - it slows everything else down and takes the fun out of SEV. If all the UI issues were magically fixed,
then AI would be the next problem.
I do have to say that I am stupified that Aaron doesn't play his games. It's a bit like an artist painting blindfold ("Hey look, I managed to get a blob of paint on the canvas!") or a builder not checking for structural integrity ("Ha! I'm not going inside that pile of junk, let someone else deal with any collapse!"). If this is the case then it's a minor miracle that SEV was even able to gain the lukewarm reviews it's had so far.
As an aside to Uncle_Joe's post, I'm also one of those who don't do multiplayer (and GalCiv would likely have been worse with it added) and I think Stardock have a valid point in seeing single player games as the majority market. Half-Life is the most popular online game according to GameSpy stats (with a peak of 75,000 players online in December '06 - see
Online Gaming Zeitgeist) yet this is tiny compared to the total number of gamers out there.