I tried to play one or two BAR games but it is just inferior in almost any way, imo. The only plus I see is better menu design. It supports only 16 players in a game; has a much smaller community; doesnt have many features zk has and we take for granted; dumb AI; no unit AI (units do not automatically kite, etc.); no terraform; not-flat tech tree is a pain, I really appreciate how easy is to plop any factory or start any building. If you wanted to want to build a something like a singu or a strider in BAR, you have to build a T1 factory with your commander (his build options are extremely limited), get a constructor, build a T2 factory, build a constructor from that T2 factory and build a strider factory with this T2 builder. And, for example, if you plopped a T1 bot factory and you want to get some T2 tank/airplane, you first have to build a T1 tank/airplane fac, then appropriate builder, and then T2 tank/airplane fac. And also, only T2 constructors can build advanced singus, a superweapon, etc.
Plus, all BAR units feel pretty same to me. I like how Zero-K really emphasizes that all projectiles, interactions, etc. are based on some in game physics. Take Sumo, for example - it destroys units by throwing them around and letting them get killed with colision damage. In BAR, there are no cool and unique units like that.