The base game is a skeleton module that contains a tutorial and two scenarios. There are currently eight DLC packs priced around $30 each. There is a robust database editor as well as map and scenario making tools that can produce quality content (which is why the absence of Steam Workshop capability is quite interesting).
The tutorial is quite enjoyable and I have played it dozens of times over the years.
The free module is worth it just for the tutorial scenario alone, and that will give you all you really need to know about the whole system. I have been playing these Airborne Assault series of games from David O'Connor for over ten years and they have never ceased to disappoint. To be honest there was a time where a Windows font issue rendered the game unplayable for many for several months; however that seems to be a thing of the past with Windows 10.
Recommendation: Get the base module as it is free. If you like what you see then some of the scenario DLC packs should be worth your investment.