I posted a whole bunch of bug reports tonight. It is all meant to be constructive feedback, and I also wanted to post some positive comments here.

STUFF I LIKED
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* The ship battles are great! I love watching the ships blasting the crap out of each other. Fleets seem to work for me too.
* Graphics for the colony window are a little better than Beta 3. More unique building icons.
* Lots of small improvements to the colony interface, especially in the "Details" window
* Ship models are looking good with textures. I'm even playing on a crappy Vaio laptop with a weak Radeon Mobility card (that GC2 reports to have less than 32Mb of texture memory). It still works until I get home to my good PC!
* Better pictures for the race ambassadors. The Human guy has hair now, so I guess I'll have to stop naming my race the Kojaks.
* Diplomacy appears to work. It seems as stable as the GC1 diplo window so far.
* Consistent display of ships and stuff on main window at different zoom levels. This was erratic on Beta 3 (zooming out didn't always display icons for all ships in B3)
* Planets on main window look great. We have a semi-realistic Sol system, complete with Earth and orbiting grey moon.
* More techs!

STUFF I HATED
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* The Miniballs look dumb on the ship combat window.


Beta 4 is actually fun to play, where Beta 3 was (as Stardock already stated) just a test of the game engine. Things are shaping up very nicely. Good stuff!