I watched this last night.
I imagine a lot of purists will be much offended by how fast and loose the movie plays with Shakespeare's text, but for me it did what every worthwhile adaptation should - it gave me a new perspective and make me think about Hamlet in a different way.
This is a unmistakably singular vision, and while the early scenes are a bit shaky in pacing and tone, it eventually becomes tense and thrilling. The conceit of the adaptation is that it turns the story into a paranoid thriller told entirely from Hamlet's perspective. This means a lot of the plotting has been excised and a lot of supporting characters have been cut and their dialogue given to other characters (not unlike Ian McKellen's Richard III). This sometimes changes Hamlet's relationship to the other characters in an interesting way. For instance, Horatio's dialogue is given to Ophelia (Morfydd Clark) and Laertes (Joe Alwyn), deepening Hamlet's relationship to them. One character who suffers from the cuts is Polonius (Timothy Spall). In a good movie or stage production Polonius can steal scenes, but here almost all of his comedic dialogue has been removed, and as a result he mostly served as the Ax-man to Claudius (Art Malik, excellent in his limited screentime). Timothy Spall does his best, but I really wish the filmmakers had found something more interesting to do with his character.
Of course, shaping the movie around the perspective of Hamlet wouldn't work if the movie had a mediocre Hamlet, and thankfully Riz Ahmed's performance is very good - especially once he gets past the mopey early scenes and is able to tap into the energy that has distinguished so many of his other performances. This is perhaps the first time I've seen a Hamlet who feels like he could genuinely be mad.
I pity the poor high schooler who watches this instead of doing the required reading, because they will be screwed. It might be hard to follow for those unfamiliar with the play, but I found it fascinating.