DirectTV version of HBO OnDemand sounds great. I've had OnDemand for Xfinity, Optimum and Verizon. Optimum was especially awful because those bastards charged $5 extra per premium channel for their OnDemand channels. At least OnDemand is "free" on Xfinity and Verizon if you already subscribe.
I can tell you for the most part all the Premium services OnDemand channels pretty much suck. It is very spotty, rare that they include a full season of any of their shows that alone multiple ones.
OnDemand should be just that, but it is anything but. Very scattershot and absolutely no rhyme nor reason how they are programmed. This is why services like HBOGo, MaxGo, etc are really good - but I do think it's crap all the hoops you have to jump through to get it. But when you can it really is pretty awesome service.
It is great but a caveat (may be important to some) is that, with Directv, you cannot get HBO to Go on other third party devices, (for example the Roku box). I don't know what the deal will be with AppleTv. Directv has chosen to offer their own version of HBO VOD equivalent to HBO to Go and to not allow actual HBO to Go on third party devices.
I can only assume that move is being made to at least try and do what they can to eliminate cord cutting.