If Beale Street could be a great movie this isn't it

I have to think that Barry Jenkins made a really bad decision in following up his AA winner, Moonlight, with an adaptation of the (last?) James Baldwin novel, If Beale Street Could Talk. Jenkins must be a huge Baldwin admirer (he dedicates the movie "to Jimmy"), as who isn't, and must have been taken in by reading Beale Street, but his very faithfulness to the novel as a sacred text from his literary hero is the undoing of the work. This movie - well-intentioned, well-acted at times (w/ particular props to the excellent Regina King) is terribly slow-paced, sentimental, and didactic, clocking in at two hours that felt like 4. I'd re-read Beale Street not too long ago, and it struck me as Baldwin's attempt to write a mass-appeal best seller while also scoring some points about the injustices black Americans experience in the legal system. Right on for this second point: Baldwin write about false arrests and the pressure to plead guilty in this book (and now movie) set in the 60s - true then, true when Baldwin wrote it (the 80s?), true today - as we all know. At least today it's better documented and made public through social media. Jenkins, hitting home of the obvious, includes a few stills of blacks under arrest and working in prison gangs, an unneeded, heavy-handed message. Overall, the pace of this movie is so slow because, in following the novel, a lot of the key scenes are elided and the only really great scene, in book and film, is the argument between the warring black families over the fate of their children, an homage to Romeo and Juliet, perhaps. In brief, the film and book begin with a young man, Fonny (sp?), in prison being told by his girlfriend, Tish (the narrator) that she's pregnant. The drama, such as it is, involves trying to get Fonny out of prison, where he's being held unjustly, the result of a police frame-up. Compare this, say, to the great series on this topic, The Night Of, and you can see how all the tension, conflict, and ambiguity is strained out of this film and replaced with what?: Many scenes of the young couple in love, having their first night of sex, setting up their first apartment, planning to move up in the world to a vacant loft space, and so on. At best, the movie is heart-driven if not plot-driven, but the end is a long time coming and leaves open far too many questions. The fault lies in part w/ the material - I'm not sure there's any way to make a great movie out of Beale Street, which is not necessarily a bad thing to say about a novel - but if there is this isn't it.