Wish the app were available on Roku, but I can still access it through my apple TV or Xbox for now. As for the actual app itself...
I like the interface better than HBO Now, but it feels empty, much like Disney+ in how quiet it is while browsing. On Netflix, you constantly have trailers playing for things which sometimes gets me to watch something I wouldn't have otherwise. I wish these other services would incorporate that as well. Having pretty much all of the DCEU in one place + pretty much all Batman movies except the Nolan trilogy is nice.
Something I find a lot of Value in is the Cartoon Network section. They have such a deep catalog that's really never been all in one place like this. I was never a fan of the Disney cartoons growing up outside of Recess. Other than that, it was either Nickelodeon or Cartoon Network, so this is nice to have. The Adult Swim catalog is also on here. The Turner Classic Movie hub has quite a bit of great old movies as well and not an insignificant amount.
I plan to watch a watch a few of the originals, although their launch lineup is kinda weak (almost weaker than D+ when you account for how big The Mandalorian hit it)... if Love Life, Elmo, Looney Toons, Cratopia, Legendary and the On The Record documentary was all they were currently releasing. HBO themselves is currently releasing it's own week-to-week content within the service and new scripted and unscripted originals will continue to be released over the next few months, unlike what Disney+ did. I do find it hard to find some content on the service though if it's not displayed on the front page. You really need to search to find some things.