Long after Hegemony Rome's release I finally had the chance to commit some substantial time to the game and unfortunately I came away mildly disappointed.
I had thought there were plans to make the AI more aggressive, but it doesn't show in the game. Enemy units only camp in their native cities and come out only to defend against small raiding parties or when the city is about to fall. If I leave undefended land on their border then they'll launch the occasional raid, but they back off if there's one or two skirmishers in the nearest fort. They never seem to attack eachother or expand. In fact, more than a year into the game I even found untouched bandit units gathered around their camp on the border of an "aggressive" AI faction. Yes, this happens even on the aggressive AI setting in sandbox. There doesn't appear to be any noticeable improvement made over Hegemony gold AI.
I was also excited for the expanded diplomacy, but it appears to be even less usable than it was in Hegemony Gold. I just came out of a sandbox game where I've captured all of Brittania by force and scouted the coast of Gaul out, but I found there was not a single faction available for an alliance. The requirement that the NPC factions have -25 hostility to form an alliance precludes quickly absorbing any of them through alliance. It's especially frustrating to see on the diplomacy window that the other faction is intimidated enough that they would actually pay tribute for an alliance but will not enter one because of the -25 hostility requirement. I would have preferred to see a requirement for a minimum intimidation level, or even a minimum amount that intimidation must exceed hostility. The in-game guide only suggests not fighting the opposing faction and waiting for time to wear down their hostility points. In 3 game years I only saw a total of 3 or 4 hostility points drop from a couple factions on Gaul while I occupied myself with Brittania. This is an incredibly slow and boring process for lowering hostility. Have I missed a way to manage hostility? If I haven't then diplomacy in Hegemony Rome is very disappointing. Right now I see it as a downgrade from Hegemony Gold.
These two shortcomings are enough to kill my interest in continuing to play, even though I really like certain improvements. The improved graphics are nice, as are the mechanics built around forts, bridges, and the new wood resource. Upgrading cities and units is great. The map is beautiful and massive, although grinding through sieges in Gaul gets monotonous since the terrain is less varied than what we saw in the Aegean world from Hegemony Gold.
My first impression of Hegemony Rome is a resounding, "meh". It fails to improve on its predecessor where it needed to most, and doesn't offer much more than an HD remake with a new setting and a handful of new game mechanics.
EDIT: I've followed up with a little further testing and found that the hostility points tick down much faster after establishing a truce with the other factions. Although, even at this rate I estimate it would take at least 5 game years at a truce for hostility to drop by 25 points. That still seems like too long a time to establish an alliance, especially since by the time you're that far into the game you can steamroll any single faction in under a year.