Perhaps Stardock could turn this question into a structured poll (at least I haven't seen such one yet) to capture the learnings to apply in future titles?

I would agree with rakenan that for me the unique techs had the greatest impact; however the AI behaves much more believably / clever / realistic in quite a lot of cases, which I appreciate more than the overall increased difficulty. So I'd say it's a really great job done on the AI on 2 levels.

Overall splendid job on the bug resolution, speed & feedback + so very nice to have listened so closely to the fanbase out here!