+++ Warning, minor spoilers ahead +++
As most know, Zach Snyder had to drop out of directing Justice League during filming due to a death in his family, at which point WB decided to make it a single, stand-alone movie, and brought Joss Whedon, who had helmed many of the very successful MCU movies to finish the movie. Snyder originally intended to have a Justice League trilogy, so when it was turned into a stand-alone movie a ton of content was cut out. And, Whedon re-shot some portions of the movie, mainly to add humor into the movie to make it "less dark" than Man of Steel and Batman v. Superman had been. The resulting theatrical version went over like a lead balloon (I think in large part because of Whedon's rumored behavior on set), and pretty much ever since the theatrical release fans had clamored for and demanded the "Snyder Cut". The result is a four-hour-long movie that shows the direction Snyder had intended to take the films.
As I mentioned above, Snyder had envisioned a Justice League trilogy of movies, with this movie split in two, and the third movie set in the nightmare world that we saw a glimpse of in Batman v. Superman. The biggest change from the theatrical version of the movie is that Steppenwolf was not really the "big bad" he was essentially a lackey trying to get back into the good graces of Darkseid, after having been banished from Apokolips. Lois's involvement in this cut of the movie is much different, and we get to see Martian Manhunter who was completely removed from the theatrical version. And, both the characters of Cyborg and Flash are set-up a lot more in this movie than they were in the theatrical version, and you get a lot more of each of their backstories (especially Cyborg).
I have the UK import Steelbook. Like the US domestic release, that one has two UHD discs that have the movie split into two parts, probably where Snyder had intended to stop the first movie had he been able to execute his original plan. The first disc has the first two hours and forty-one minutes of the movie, and the second disc has the last hour and a half (approximately, excluding the credits). The UK import also has a 24-minute making-of feature that details how the Snyder Cut came to be and included interviews with the cast and crew. Unfortunately, there is no commentary track on the movie. The UHD discs are region-free and will play on US players, and I believe the regular Blu-ray discs are region-2 locked. But, there are no additional extras on the regular Blu-rays so you really do not have to watch them.
Overall, this cut of the movie is better than the theatrical version. While I do not think the theatrical version is as awful as some paint it, it is definitely a lot more flawed than this cut (which, admittedly, has its own flaws). There are rumors that WB might actually restore the Snyderverse and let Zach Snyder make the third installment of the movie, but for now, the theatrical version is the official DCEU canon. I personally like the darker, edgier tone that this movie takes (it is rated R, mainly because of a couple of f-bombs that get dropped), and respect that they did not try to be a carbon copy of the MCU movies. That said, Ezra Miller's quips in the theatrical version were great, and while a couple of them made it into this one (including wondering whether Wonder Woman would go for younger men), that is really the only thing I missed from that version. This is definitely worth checking out.
