Star Trek: Into Darkness wasn’t a bad movie at all. I’m not sure that it was better than Iron Man 3 if we’re talking overall movie quality, but they’re fairly different movies.
The piece of advice that I heard about the movie that really made the most sense was to consider how low-budget the original Star Trek movie were compared to other films at the time. The dialogue could have been written for a television show and not a movie where everything needs to be explained within two and a half hours tops. The first J.J. Abrams movie set the stage for whatever films followed this one, and the other films in the TOS-era films and TNG-era films served to supplement the television series in a way that could sell tickets in cinemas.
And that’s what this second film is: it’s fan service without apology and it doesn’t give a fuck. Its story solidifies what made the previous Kirk/Spock such a dynamic duo among dynamic duos in its own way.
If you enjoyed the first film, you owe it to yourself to go out and see this second one. If you nitpicked the first film to death and ended up not liking it, stop being a try-hard movie critic or overly-devout butthurt TOS/TNG fan and go watch the J.J. Abrams films as back-to-back as possible.