Finally tried it, no need to rush. Not much to compare against, the tank sim market is practically dead, so the closes comparison would be Steel Fury and Sabow from decade ago.
Steel Fury allows you to take any crew position inside the tank. Even loader, although you can't do much as loader. But as commander, you can actually command the tank without the need to aim and drive all by yourself, the proper tank commander routine. No such thing in GHPC, you are the gunner, commander is mostly for help and driver is nonexistent.
Because in Steel Fury you tell the driver where to go and how fast. You can use commands to go to the next waypoint or drive only on the roads, or keep the given movement speed. GHPC gives you direct control over driving and has cruise control option. Quite arcadey.
I would put the lack of available commander seat as a major disadvantage of GHPC. In Steel Fury, playing as gunner (classic tank sim way) vs playing as commander gives you quite different experience. With modern tanks, this could be even more interesting. Direct driving is not particularly good too. I don't think this would be changed; while GHPC is still a beta, the core gameplay is already here.
Another nitpick is that you can't traverse the turret by keys in GHPC, only by mouse. Steel Fury, in fact, not only allows you to use either mouse or keys for traverse, but also has (if tank had it) two traverse speeds, manual for precise movement and powered for quick movement. Modern tanks don't use manual traverse much, but having mouse for precise aiming and keys for quick movement would be nice - and this could be easily added to GHPC.
Otherwise it looks really promising, and with lots of potential - after the main game will be considered finished, they could add expansions for other theaters, like 1973 war or Iran-Iraq war. Gunnery is already very solid, and if they add more legit fire control features, it would be even better