This is a great expansion as it adds oodles more cards to the game, really making things interesting. You start to see some cards with costs more than the previous max of 6, and in general the game starts to feel a bit more epic.
As for the added gameplay feature of being able to capture other player's cards through military conquest, this aspect was decidedly a disappointment. It's a bit of effort just figuring out the mechanics of how takeovers work, because the rules are a bit strange, and more work still maintaining a constant count of your military strength as you play using the included sliders and marker pieces. And in the end, only one out of every few games involves ANY actual takeovers, so all the work has very little payoff, and I find it easier to play without takeovers active. The one interesting effect takeover rules can create is an ongoing arms race between two players, who continue to bolster their defenses back and forth, but never end up attacking.
All in all, I'm very happy to have purchased it, I just wish the conquest mechanics were more worthwhile. Perhaps a future expansion will make it more interesting?