When David (Mark Ruffalo) sublets a spectacular San Francisco apartment he doesn’t think to ask questions as to what happened to the previous owner. All he wants is a decent couch and a color television, nothing else really all that important to the depressed former landscape architect. But when Elizabeth (Reese Witherspoon) starts making appearances claiming she’s the rightful tenant, David’s curiosity as to who lived in the space before him is understandably piqued, especially when the pretty young woman starts walking through walls and standing in the center of coffee tables.

Soon David comes to believe he’s being haunted by a ghost, taking it upon himself to befriend Elizabeth and help her make peace with whatever it is that’s preventing her from passing on. The thing is, she remembers nothing of her mortal life, and it is only together that the two of them can figure out what is going on with her. It soon becomes apparent to both of them something is developing between them far more involved then friendship. Still, what chance does love have if only one person is actually alive, the other stuck somewhere in-between the living and the dead?

The breezy and mercifully short romantic comedy “Just Like Heaven” is a hodgepodge of so many other movies it is nearly impossible to figure out what its own identity actually is. Part “Ghost,” part “All of Me,” part “The Ghost and Mrs. Muir,” and all of it mixed together with equal sprinkles of “The X-Files” and “Highway to Heaven,” if there is an original thought or idea inside Peter Tolan (“Analyze This”) and Leslie Dixon’s (“Freaky Friday”) adaptation of Marc Levy’s novel If Only It Were True I certainly couldn’t find it. It’s a tired mess of clichés and ideas compounding one upon the other, and as hard as everyone involved tries to make it seem otherwise the whole thing ends up being nothing more than an overlong bore.

Shame, because both Witherspoon and Ruffalo deserve better. Each dives headfirst into the respective roles, investing them with far more zest and zing than the parts probably warrant. Better, the duo has a nice, easygoing chemistry that’s instantly intoxicating, providing far more in the ways of laughs and smiles than I’d usually expect from an enterprise quite this bad. They are, without a doubt, wonderful, and if I was going through a bout of late-night insomnia and ran across this on cable TV I might actually leave the movie on based solely on the two actor’s combined charm.

If only “Just Like Heaven” was actually worth their efforts. Even when things have gone wrong for “Mean Girls” and “House of Yes” director Mark Waters (“Head Over Heels” comes to mind) he still manages a subversive wit that, if not always appropriate, is still good for a laugh or two. This time, however, Waters shoes no sense of style, no flair, no originality, the only constant in his handling of this just how remarkable unremarkable it is. He even wastes “Napoleon Dynamite” star Jon Heder, the actor relegated to a throwaway part that’s ultimately no more than an uninteresting afterthought.

By the time the requisite four-hanky climax I upon us, it is downright remarkable how completely unoriginal nearly every facet of “Just Like Heaven” really is. There is so little worth remembering, so scant moments I can actually recall, that by the time I made my way back to the car I was almost shocked to discover I could hardly remember a single worthwhile scene. Well, I did remember one thing, and that was how snazzy the shoes were that Witherspoon wore for nearly the entire picture. Getting a pair of those wouldn’t just be great, it might just be heaven.