The Snyder Cut of
Justice League won't be out until 2021. HBO Max planned to have more original content ready at launch, but the pandemic obviously got in the way. That said, their existing back catalogue/library is pretty impressive...
Basically, it's all things HBO / TBS / TNT / Warner Bros.
In terms of TV, it'll be HBO's entire library (some of which will apparently be 4K for the first time) + notable series like
Friends,
The Big Bang Theory, and
The Fresh Prince of Bel-Air, along with all shows ever produced by TBS and TNT, in addition to every other Warner Bros. series ever made.
In terms of film, it'll be all of the DC films (from the Reeves
Superman films to the Keaton and Nolan
Batman films to the DC movies of today), along with the
Conjuring,
Godzilla,
Harry Potter,
LEGO,
Mad Max,
The Matrix,
Ocean's, and
Rocky franchises + all other Warner Bros. films/franchises (which you can find
here (1918-1999) and
here (2000-present).
Personally, HBO Max has more value to me than Disney+ and maybe even Netflix. Once they start releasing HBO Max-branded original series on a regular basis (which, again, will be separate from the HBO brand of shows), I have a feeling this will be the streaming platform I use more than any other.