Such characters are perfect for shorts, which is also why the included short films on the Despicable Me home releases were well received, particularly the Banana one. As such the same idea applies to the Minions film. They've essentially taken the short gags and stitched them together to make a feature length film. The plot is wafer thin and only a vehicle for a bunch of skits featuring the Minions. I would not say this is to the film's detriment, as I suspect those heading to watch it will be getting exactly what they expect out of it. But if you're expecting something more, then you'll be left wanting.
The Minions it turns out were some particularly evolved creature whose only goal in life is to be at the service of the biggest baddest foe on the planet. So we follow them from their incarnation in the opening credits, throughout history up to the era of the 1970s where, finally bored of their isolation, three of them head out on an expedition to find a new big boss. This leads them to America where they stumble upon an advertisement for a secret villains convention that will host the biggest and baddest criminals from around the world. There they find themselves in the service of a celebrity villain who sets them out to steal the crown of the Queen of England. There surprises, betrayal and general frivolous nonsense awaits.
There are a lot of laughs to be had and the Minions will indeed satisfy their fans and sell much merchandise. What should be highlighted as always is the excellent job the animators and voice actors do of bringing these little guys to life through visual expression and sound to perfectly communicate everything these guys feel and say in a language not understood aside from a few words here and there mismatched to the situation for comical effect. As such the animators deserve recognition. There's even a cool stop-motion portion in between! The gags also work well enough. But outside of the Minions themselves, the other cast is utterly forgettable.There is no other great character on par with Gru or Agnes from the previous films, but otherwise the movie delivers using the characters it advertises. This is their movie. Which isn't to say surprise cameos can't be found!
So if you're in the need for an hour or so of good laughs, then this is the comedy of the summer. If you want something more from your animation, go see Inside Out instead.