All people around talk about UI horror... As for me, I didn't find it SO horrible, it's BEARABLE. The worst thing I found in this game is space combat, rather ugly comparing with other parts of game. All the rest, combined with mods, makes MoO3 very decent series follower IMO.
I am a HUGE fan of MoO2 but never really played MoO1 at all.
The features that MoO2 had that made it so enjoyable to me were, Race customization, Ship Design actually mattered in combat, and research choices had a BIG impact on the game as a whole.
I loved the fact that you could have Armor Piercing weapons and run into someone who got Heavy Armor just to mess you up hehe.
The only thing I found kind of annoying was in mainly 3 things. Ship Drives, Shields and Armor. Mainly the fact that lets say you skipped shields all the way upto Class V (5). Your spies would still take the trouble to steal classes 1 and 3 if your opponent had it instead of realizing that getting those was completely pointless. Same thing for Armors, they would steal crappier than what you already had or ship drives.
This was my only real complaint about this game at all and when you think about how big it can be that is a huge compliment to the developers. Especially since I believe those could have been fixed without to much trouble if they decided to, although perhaps it was left that way deliberately on purpose for balance.
Sadly MoO3 made me regret wasting my 10 bucks and my time on it and to either repurpose that CD as a coaster or a frizbee lol.