Phoenix, a weird dude anyway, does an incredible job with the character. He totally makes it his own and does not try to be a carbon copy of any of the performances that have come before him. It is unclear where the movie fits (if at all) into the DC movie and television universe. Obviously, Jared Leto played a totally different version of the character in Suicide Squad, and this version is not a precursor to that one. It does not give anything away to say that the movie is set when Bruce Wayne is still a child, so we do not get any hint of Joker vs Batman.
The 4k set is a two-disc set containing the UHD disc and a regular Blu-Ray disc. The UHD disc just includes the movie, and the extras, which consist of about half an hour of making-of and behind-the-scenes material, are included on the regular Blu-ray disc. The only disappointing thing about the physical release is the lack of bonus material. Even though the movie does create something of a continuity mess with the DC cinematic universe, even more than it already has been to this point, if you accept the fact that it is its own thing and does not (at least as of now), and may never tie into the other movies, it is definitely worth checking out. It is well-written, acted, and paced. The two hours do not drag at all. I highly recommend it.