I've bought recently the DC bundle, I should have done it sooner, as I enjoyed AT some time ago...Very good games !
But it seems like each game is "stuck" with its own engine version, so you don't have for example sea transports in WTP, interface is a bit different, etc...
As I suppose -and hope- the team will create more games in the series, it will be more and more useful to have them share the same updated engine, instead of having increasingly obsolescent games.
That's what kept the Panzer Campaigns series alive, BattleFront does this with their CM2-WW2 engine, here Ageod also does for their Roman games.
Is that planned anytime for DC ?