Given how Important it has been for world history it is surprising that hardly any strategy game focuses on this time period.
I feel that a Total War game set in the Levant from 630 to 700 would be very interesting and fun.
Mostly because the arabs focused on light cavalry, tough not in the same way as the Mongols did, and had the luck of finding both their greatest existential threats, the Persian and Roman empires, exhausted from a long war and decimated by a plague.
A mechanic that simulates the spread of the plague and how it weakens more the settled nations than the nomads like the arabs would be much needed to balance the starting situation, after all the arabs were not incredibly superior soldiers, but had luck and good generals on their side.
Also to note is that arab warfare was mostly made up of raids, a mechanic to allow raiding the infidels unless they convert or pay a monthly tribute could also be introduced.