THE PREMISE HERE isn’t bad. First, of course, there’s the comfort element: we get a Loner Drama with a “House”-like charismatic figure, this time the head of a mental ward. Then, there’s the twist: the show goes inside the heads of seriously messed-up people, dramatizing fantasies of, say, invading flying saucers. Sounds decent. But will it be a hit? We have reservations about lead Chris Vance (“Prison Break”), who seems a bit low-key in comparison to charismatic counterparts Simon Baker and Hugh Laurie. But we like the flashes of edginess in the trailer. To cite one example, Vance’s character tells a colleague to have a nice day and leaves, after which she says, following a nice pregnant pause, “Dick.” Humor like that could keep this one from becoming another forgotten Summer serial. But given its relative lack of originality “Mental” will have to introduce some fun insanity to survive.