So I played a couple of games vs AI in beta 4, and I would like to share my thoughts. Which are mostly on some specific aspects of the general feel of the game, so that's why I didn't put it in the technical/gameplay feedback thread.
Last time I played was around beta 2. Just one or two games before I decided beta testing really wasn't for me, and went back to supreme commander. So consider me a noob!
First off, the game really feels a lot more fleshed out. I love the pirates, improved tech tree, zoom to cursor etc. etc. etc. However, I don't love the fact that there are two types of research stations. Maybe I haven't played enough but it feels like a artificial way of giving me more stuff to do.
I really had a lot of fun the first few games (which I didn't really have in beta 2, so kudo's there) right up to the moment where I figured out how to always beat the AI. Which was a lot harder than in beta 2 by the way. I guess enough has been said on AI so on to the next point.
Combat: I haven't played enough to comment on balancing etc. What I do think though is that the movements of the ships is a bit... not so space-like. More underwater-like. How about having the TEC ships move in a more angular way, to represent thrusters (which you would of course see when zoomed in close enough). Then you could have the Vasari move in the more smooth manner all ships move now (different alien style thrusters or whatever) to create a more different feel for the factions. Or how about a class of slightly-bigger-than-figher ships that still zoom around instead of hover (I'm thinking of homeworld of course). Probably too late for that though

Oh and formations! Please don't forget about formations.
Also, planetary upgrades could use some work. I don't object to the whole management of planets being abstracted down to one or two upgrades (although I'm more a 4x person than rts). But it should feel like you are really improving the infrastructure on your planet. Changing the description and the picture of the button you press so it feels less like just upping some statistics would probably help a lot. Maybe it's just the placeholders?
Other than that... can't think of anything that hasn't been said a million times. Except that performance is really, really good. I can play the game on my laptop without a hitch! Amazing!