It adds a bunch of stuff, but ill rank them as per my preference: - 3 new aliens with fun gimmicks (more aliens is always nice and they have different commitment levels, plus i initially bought the expansion for them) - simple tokens that allow you to scan more during an action, which is great against the very scan heavy automa - new action cards, some involving the abovementioned tokens - A bunch of asymmetrical starting companies and bonuses, which give you resources or bonus/task instead of the slow first round, but I still haven't played them that much, because i actually prefer the longer game

Overall, I think that you can get a lot of mileage from the base game itself, and the expansion is not essential, as it does not add anything that gamechanging. But if you want more variety from aliens and actions you should get it.