Some explanation:
Ego Draconis ended halfway through the story, where most stories have the "turning point" moment. The expansion pack continues and supposedly (I haven't finished it) completes the story. This is in itself a questionable decision, probably driven by a lack of budget; possibly by greed: for the early adopters, the price amounts to $70 for the full game, or upwards of $100 if you were unlucky enough to get it on 360 both times. I got it for $20 during the Steam sale, and have quite enjoyed it so far.
As far as gameplay is concerned, I can't speak to the 360 version but the PC version plays just fine - like a slightly-more-open version of a cross between Dragon Age and Oblivion. It also looks rather fantastic (on PC, at least), although I can't speak to the graphical quality on the 360.
So, I'd say it's better to get it on PC, as that's its home platform and I can't think of any benefits the console version offers; but it's not a bad game overall, at least now that it doesn't end in a cliffhanger worse than Halo 2's.