While I certainly enjoyed the film for it's attempt to make it character driven, I was a bit disappointed by certain elements that tended to contradict the first film.
For example, the relationship between K and O I felt was a complete retcon to the first film's depiction of K longing to be with his wife again. At first I thought this relationship was a new thing after K came back to MIB, but as we see in the 1960s segments, it's been going on for much longer than that. Did the writers just forget K had a wife during this time, or did everyone involved with the film HATE the wife subplot that they're trying to erase it from the franchise entirely? I hated how they wrote in that K's wife left him in-between Men in Blacks 1 and 2, and now with Men in Black 3, it's like it never happened.
WE HATE THE WIFE PLOT! ->

<- Me
But overall, I thought it was a good film. The best parts for me was when the movie focused on Josh Brolin's depiction of Younger K. That was refreshing.