It's cute, but not great. Everyone loves the Minions, but overexposure can cause people to turn on a dime faster than you know (see any one-two hit wonder for example). The Minions are great supporting characters (See Despicable Me 1 and 2) and having seen their "solo" movie that's just confirmed. They are funny, but just not enough to carry a movie. They are truly second bananas. There are a lot of fun bits in this movie, just not quite enough to carry it's relatively short running time.
So it deals with the origins of the Minions, and why they need a boss to feel complete. It's set in 1968, which if according to my somewhat questionable math would make Gru even older than me when he gets married in the second movie. Perhaps I shouldn't worry about that sort of thing. So they go to Villain-Con to find and work for a new boss.
Since I was at Media-con the day before, this part was quite funny. And yes, I'll have reviews being posted in the next couple days. Kind of fun to be without computers for a while. Set in 1968, the soundtrack is so much better than the first two movies, that I have to say.
Anyway, I liked the movie. The trailer for the Jem movie looks horrible, and I'm not even that familiar with the show.