It is possible to play ATF like BCT. However, you will miss out on alot of new features. I would say ATF is a new game though over BCT.
A major fault for BCT were poor interface, and lack of tactical debt. While, tactics dominated the game, luck was a superior factor. You couldn't control formations, give specific mission orders. It was line your forces up and go.
ATF changes all that. Alot more is automated, yet still providing you with the opportunity to micromanage. You can select formations, assign missions, organize your forces, direct fire, and synchronize & mass fire from a more friendly and intelligent interface. 3D maps provide you with the ability to more accurately assess and employ the terrain to your advantage.
The AI is far more intelligent in ATF as well. They seem to react more to the situation as it develops. Unlike in BCT, where you could plan your mission and continue while rarely stopping the clock, in ATF, stopping the clock often is mandatory to maintaining situational awareness.
There are some drawbacks though. First and foremost is the lack of a large vehicle database. I bought BCT: Commander when it first came out. So I've always played with all the add-ons and Construction Set. ATF lacks the MLRS, utility helicopters, and a some other vehicles that would make a more complete game. We are awaiting the release of the Database Editor. I believe it will be critical to attracting the attention of international players.
BCT focused on the platoon to Brigade Level. ATF is section to Battalion. I believe there is no limit to the amount of vehicles and units we can add in the scenario editor. However, stretching beyond battalion level could exceed the limititations of many PCs.
The game appears to demand alot of CPU, particularly as fighting heats up. I find this is usually the case when you max zoom in showing all vehicles. (You probably shouldn't apply this option in any case because the fight gets confusing.)
Overall, ATF is far better than BCT: Commander. Things like hotkeys make gameplay more interesting. Since you can assign missions to various units in your force, it feels far more realistic. Yet, if you are a scenario builder like I am, for now, BCT: Commander will be a nice temporary supplement.