Discussion of Roman expansion - beyond OTL's limits, tends to focus primarily on Germania and secondarily on Persia.
But what about other directions-
For instance, down the Atlas mountains to encompass all of Morocco?
Nubia and Ethiopia, possibly with the Somali coast?
Arabia, or at least its coasts in the west (down through Hijaz and Yemen) and/or the east (over to Oman)?
Comprehensive conquest of Crimea, sea of Azov and southern Ukraine?
Northern Caucasus?