If you can get your hands on it I'd really suggest buying Ground Control 2. It's not an rpg, but the bugger has one of the best space opera-plotlines I've ever seen. I know one mag editor made a comparison with Freespace, that my friend is a one-of-a-kind honor. The game is also very tactical, fairly realistic, has variety and, most importantly, is damn fun.
Too bad the multiplayer element is a bit lacking. Otherwise GC 2 would have gone to share the stars with such games as Medieval: Total War, Starcraft and Dawn of War.