Unfortunately, it's had something of a rocky start. The service is available only from select cable/satellite providers, and only on certain devices.
For example, HBO recently updated the HBO Go Android app to support devices running Android4.0 (Ice Cream Sandwich). But tablet users? Outta luck.
Not for long. As PC Magazine reported last week,HBO Go for Android tablets is in the works and "coming early this summer," according to an HBO spokesperson. The updated app will be "optimized for most Android tablets, including Kindle Fire."
The bad news? Same as always: You can't just buy HBO Go a-la-carte. If you want this awesomeness for Android, your Xbox, your Roku box, or the like, you must subscribe to HBO via your cable/satellite provider. And although most of the major ones are now carrying it, there are still some holdouts.
In fact, Comcast subscribers still can't get HBO Go via Roku, which annoys me to no end. But Comcast does support the current Android app (along with iOS versions), so there's no reason to think the upcoming update won't.
And I'd be surprised to ever see the app on an Apple TV, though there is a way to watch HBO Go on an Apple TV, sort of.
Personally, I'll be very happy to add HBO Go to my Kindle Fire. Between that, Netflix, and Amazon Prime, the little tablet will offer a better TV selection than anything else I own.