Interesting TL. I would like to see something more on the emerging syncretistic culture of the empire, though. In OTL the Hellenic element remained rather aloof of the natives, reinforced by migration from Greece, and what "Orientals" there were among the ruling classes had become (at least outwardly) hellenized. Also, how is Zoroastrianism doing?
I have however one rather major nitpick, namely the traditional cliche "Roman legion always beats Macedonian phalanx". The Romans, including during the Punic Wars, used volunteer citizen troops, who were then disbanded after each campaign. This means that, unlike the permanent professional Hellenistic armies, they had a problem of fielding seasoned, well-disciplined and well-trained men and units, or providing them with experienced leadership. It was only the extraordinary duration of the Punic wars that made several tens of thousands of Roman soldiers into hardened veterans and their generals adept in handling them. These were then the troops that defeated the Hellenistic armies in Greece and Anatolia, although even then in many cases it was a pretty close thing. If the Roman system had greater inherent flexibility, it was also limited to infantry. In cavalry, the Romans were hopeless, let alone when facing heavy cataphract cavalry, and as for "modern siege engineering", it was the Hellenistic states that led the way, not the Romans. A good read on the subject, if you're interested, is Goldsworthy's "The Fall of Carthage".
I have however one rather major nitpick, namely the traditional cliche "Roman legion always beats Macedonian phalanx". The Romans, including during the Punic Wars, used volunteer citizen troops, who were then disbanded after each campaign. This means that, unlike the permanent professional Hellenistic armies, they had a problem of fielding seasoned, well-disciplined and well-trained men and units, or providing them with experienced leadership. It was only the extraordinary duration of the Punic wars that made several tens of thousands of Roman soldiers into hardened veterans and their generals adept in handling them. These were then the troops that defeated the Hellenistic armies in Greece and Anatolia, although even then in many cases it was a pretty close thing. If the Roman system had greater inherent flexibility, it was also limited to infantry. In cavalry, the Romans were hopeless, let alone when facing heavy cataphract cavalry, and as for "modern siege engineering", it was the Hellenistic states that led the way, not the Romans. A good read on the subject, if you're interested, is Goldsworthy's "The Fall of Carthage".