Does this slow the game down much? Mine is on pre-order with Thoughthammer so I don't expect to see it until next week.
Not at all, as a matter of fact we seem to play through the card deck with the new explore powers much quicker. RvI seems to complete and round out the the base (with out playing takeovers) game and gives more paths to winning the game. I really like what this expansion has done for RftG. Play several games and you will see what I mean.
I plan to give the takeover phase a try once I have played a few more games with the new RvI card set. That may or may not slow down the game play. We will see
IMO I don't need to ever play the takeover part of RvI to enjoy RftG with this new expansion.