AJE is a really excellent game of the Roman era. With its added DLC kind of games it covers the whole darned time of the Roman growth and fall.
As to your question, the sale is a great time to get this game, but I would buy it even without a sale.
If you think about CW2 or Wars of Napoleon, there is a major different, this game uses the command system of all AGEOD games which are pre-corps organization, just the leaders and their qualities, no subordination. Also, no depots or supply chains, instead, simple supply.
There is a replacement page in the ledger and there is a recruitment option for building new units.
Diplomacy is very different. For most scenarios there is no diplomacy as two or three factions just go to war with each other. But when there is diplomacy, it is handled in an options presented in the ledger. that is, you select options if you have the EP or money to bribe or join others to your coalition.