From what I gather from interviews etc - the UC is pretty much the "complete" version of the film, essentially it was scripted and material was filmed to in the end be a 3hr film. It's a similar case as Watchmen - Snyder presented this cut at the first friends and family and test screenings (and it tested positively unlike the theatrical cut), then the decision was made to cut it down to 2:30 because of number of screenings, IMAX limitations and so on, and Snyder worked on this cut almost in parallel with the theatrical, once that version was done he worked to finish the VFX and score for the UC, which he did around early March actually. What really shows the film was more or less intended to be this long - most rough assembly cuts of 2:20-2:30 long films are around 3 hours long - according to an interview with the editor David Brenner, MoS' was 3:30. The Russos also said CW's was 2:40 actually. BvS' on the other hand was 4 and a half hours, and he admits there was a whole lot more in the script than the theatrical cut. The 182min UC is essentially that 4:30 assembly cut but with the fat trimmed out in the way you'd expect for a film usually. It's just for the theatrical they then had to go in and take storylines and connective tissue, stuff like establishing shots etc out and re order things like Luthor's introduction as well, which was originally supposed to happen later on.
It's not even actually rated R in Germany lol so don't expect much in terms of violence etc. Apparently the full Africa scene is what pushes it to an R in the US.
