Galactic Civilizations is a better MOO than MOO3, that's my first impression having played the game for about a week now. I haven't played MOO3 and based on the overall bad reviews of it I will stay away. StarDock's game definitely has that "just one more turn" appeal that hypothecially may keep you up until 3 AM. Here are some of the things they've gotten right:

• No ship design: at first I thought I'd miss this feature but I don't - as you research new weapons and improvements for your ships they're auto applied.
• Starbases: you can build star bases in sectors and customize them with different modules that give different bonuses to ships or colonies in a sector.
• Governors: no AI governors but you can customize each governor's build list in essence giving you "global queues" that each planet will build to.
• Internal Politics: besides managing diplomacy with other races, you have to keep your own party in control of the Senate by keeping your populace happy.
• Race customization: even though you can only play as Humans, you can customize pretty thoroughly the bonuses for your species. So you can play as super-researcher humans or bad-ass warrior race humans or whatever.
• Did I mention the huge tech tree to research?\

Initial Concerns:\

• Ship to ship combat doesn't seem to have much of an element of luck to it.
• Sucks you in for long periods of time\