This is, of course, the second movie in the Christopher Nolan directed and Christian Bale led live-action Batman trilogy which not only revived the live-action Batman franchise from near death, but arguably paved the way for the historic run of superhero movies that is still going strong today. The fact that Nolan took these movies seriously, coupled with the fact that the first Iron Man movie (which came out the same year as this) was so well done really took superhero movies out of the "cult following" that had been the majority of their fanbase and opened the genre up to wider appeal.
This movie is set about a year after the events of Batman Begins with Batman having terrorized the city criminals and inspired lackluster (to say the least) copycat vigilantes. Gordon (played again by Gary Oldman) is now the head of the major crimes unit (cleverly nicknamed MCU) which is trying to take down the mob and "capture" Batman. Joker (played brilliantly by Heath Ledger) offers his services to the mob to kill Batman and get the heat off of them put on by Gordon and new Gotham District Attorney, Harvey Dent (played by Aaron Eckhart). Michael Caine and Morgan Freeman also reprise their roles as Alfred Pennyworth and Lucius Fox, and Eric Roberts joins the cast as mobster Sal Maroni.
Aside from Ledger's casting, which was controversial when it was announced, the other big casting change from the first movie was replacing Katie Holmes as Rachel Dawes with Maggie Gyllenhaal. At the time, it was speculated the Holmes' marriage to Tom Cruise and participation in Scientology was the reason, but Nolan has gone on record saying that she was simply not available to do the sequel. Whatever the reason, while I personally would have preferred for Holmes to return (mainly because I am not a fan of recasting).Gyllenhaal does a good job with the role.
This set has three discs, the 4K-UHD disc that has just the movie itself, a regular blu-ray disc with just the movie, and a second blu-ray disc with most of the special features. The regular blu-ray disc does include a making-of documentary called Gotham Uncovered, and the movie can be played with a picture-in-picture option that includes some of the material from the Gotham Uncovered documentary. The rest of the features are on the second blu-ray disc and include a featurette on Batman's tech, the psychology of Batman, a series of Gotham Tonight episodes, hosted in-character by Anthony Michael Hall's character from the movie and featuring some of the other cast members, and the trailers, and a gallery of the different Joker cards.
Overall, the movie is great. One of the best superhero movies of all time in my opinion. While Ledger was only in the movie for a minimal amount of screen time (all totaled), he dominated pretty much every scene he was in, and his appearances were spaced out well so it seemed like he was in the movie much more than he was. The only thing I would have done differently is [SPOILERS AHEAD] kept Two-Face for the next movie. Maybe make him disappear and then exact revenge in the third movie instead of killing him off after only four scenes. From what I had read, the plan was originally to bring Joker back for the third movie in some capacity. Of course, Ledger's death shortly after filing wrapped made that impossible and by that point, the movie was finished and it would have been too expensive to go back and totally change the ending.
Regardless, the movie is great and the A/V quality of the UHD disc, especially in the IMAX scenes is wonderful. It is definitely worth the upgrade to the 4k blu-ray.