The difference between a series episode and a movie is that, even if they are connected, the film attempts to provide a standalone story that anyone can enjoy. If you are a fan of the series you will enjoy the parallel story and the hidden gems, if you are not you might like the film and try the series. Unfortunately, Hathaway is not that.
I don't enjoy Mechas that much and the only reason I watched this was that I thought some of the Mecha stories were good stories. I can't complain about the story too much, other than it was filled with hard to believe coincidences just in order to keep the same characters in focus, but without being familiar with the stories you won't get what this film was about. Characters pop up, complete with names and former connections to existing characters, and you are supposed to know who they are. The world is not developed at all. Everything stands on your ability to have seen, liked and remembered the preexisting content. And to top it off, there are two battles in total involving Mechas, one of them seen from the standpoint of civilians running around dodging debris.
The animation was good, without being exceptional, the acting was OK, but I didn't get anything out of the story, didn't empathise with any character and I do not feel the need so see what happens next. All in all it was pretty boring.