I can go on and on about Sword of the Stars + Expansion. In short, when it comes to planet improvements it's a simplified model akin to MOO1. The tactical battles are awesome and the races feel pretty different due to their different propulsion techniques. Since what research is available is random, the game can change a whole lot between 2 games which is a good thing. Also, the demo doesn't really do the game justice, if you are interested, try it through other means before deciding if it's something to like. They will also release a new patch and a Collector's Ed. with game + expansion and some extras, among other things a novel by the woman who wrote all the excellent fluff for the game (Also wrote the Arcanum manual). If you some day want to buy the game, then you should definetely get the Collector's.
Stars! is another pretty good 4x if you can stand pretty much non existing graphics. It's very involved and micro heavy, and there's a lot of math in there. Some people love the game to death, which I don't. Still, it's a pretty decent game if/when you have the patience to play it.
Imperium Galactica 2 is another pretty fun game despite its realtime nature. It features simplified Sim City like planet development, simplified RTS ground battles, and decent RTS space battles. It also has an interesting spying system and an actual story. I had great fun with this one back when it came out.
Also, I keep hearing from all over the place how MOO3 can be an enjoyable experience with fan patches and mods (Chocolate, Strawberry and all those). While I remain doubtful, I'll probably try it sooner or later.
Finally, I have had pretty good fun with Birth of the Empires during the last few days, it's quite rough around the edges though, but if they continue improving it I don't doubt it could be a real gem. The price is as cheap as you can get, and since you are German you probably don't have to suffer spotty translations and lack of documentation.
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