I went to see the movie last night, and it was alright. While watching the movie, it's readily apparent that the movie had a bit of a storied production cycle. For the uninitiated, Zack Snyder's daughter committed suicide during production, and he ended up stepping down as director. WB got Joss Whedon to finish the movie in his place. From what I heard, the movie used to be quite a bit longer at around 2:45, but there was apparently a huge push to get it under 2 hours... and it is barely less than two hours.
Probably what stood out the most in the movie was the CGI. I don't know if they had scheduling conflicts with Henry Cavill (Superman's actor), but he was CG'd in quite a few scenes even outside of fight scenes. Although, the fight scenes stood out a bit, because Wonder Woman also has a decent amount of movement in her fights, and the CG doesn't stand out nearly as much.
If I had to say what was my least favorite part, it was probably The Flash. I got into The Flash back with the original TV show starring ol' John Wesley Shipp. It seems like DC took the complaints to hear that Marvel movies are funnier, and they decided to make Justice League a bit more light-hearted. Well, the problem is that none of the heroes in the movie are known jokesters. Heck, the only hero that I can think of that would really fill that role would be pre-Specter Hal Jordan, and I don't know if they want to touch Green Lantern again just yet. (It's not really a spoiler, but the Green Lantern Corps is seen in a flashback... so DC hasn't forgotten about them.) Anyway, The Flash was pretty much turned into Spider-Man with the sort of goofy, quippy attitude, which really isn't the way Barry Allen acts in the comics. Maybe it bugged me because it felt like The Flash and Aquaman were fighting for the least useful hero throughout the movie.