Paradox didn't exactly have the best launch with Imperator: Rome but hopefully some of the most pressing issues will be sorted soon.
Speaking to Paradox last night, they said to me "I believe there is a patch planned to be released next week; as always if internal testing reveals new problems it may be delayed, but that is the plan at present as I understand it!" so unless something major happens, we should get a better experience next week.
The most annoying issue for a number of Linux users, is that the game will refuse to run unless you turn your networking off. You don't have to turn it off for your entire desktop session though, you can disable it in terminal just for Imperator by doing something like this:
unshare -n '/Imperator Rome/game/binaries/imperator'
Debian/Ubuntu based users may need to use sudo, as it seems by default normal users don't have access rights to do it. Do so at your own risk, if you think it's too risky you can disable networking your normal way through whatever network manager you use.