I have to agree. Avorion feels like a game I've been waiting for for a long time, and I've played most of the games the OP mentioned, though I'd have to say Freelancer has the strongest vibe for me, with X3 influences coming in second.
I'm coming up on 120 hours played now, and as fun as the game is in its current state, what really blows my mind is when I imagine what it'll look like next year, or 2 years from now. Fully functioning AI economy? Player empires and systems changing hands in faction warfare? Multi-station factory complexes? And it feels like that's just barely scratching the surface. After seeing the kinds of things modders can add to games in the FTB-sphere, entire new systems of gameplay and tech trees and layers upon layers of more STUFF to do... the potential for modding in this environment that Avorion provides is mind-bogglingly cool.
I can't wait to see where this is all going, because this is gonna be good.