With her bright smile, down-to-earth demeanor, and effortless ability to seem both silly and intelligent at the same time, Reese Witherspoon (2001's "Legally Blonde") is an ideal actress when it comes to playing comedic and romantic leads. There is a vulnerability about her, but also a strength and endearment that makes you like her and want her to live happily ever after almost immediately. With that said, Witherspoon is in top form in "Just Like Heaven," a supernatural-flavored romance directed by Mark Waters (2004's "Mean Girls") that gives her a full range of emotions to play, each one of which she delivers with wholehearted commitment and believability. It's too bad, then, that most of what surrounds this supremely radiant performer is either lame, cornball, or both.

San Francisco doctor Elizabeth Martinson (Reese Witherspoon) is such a workaholic that she hardly has time for anything but, a fact that has begun to make her long for something more, including a possible relationship. While driving to her sister, Abby's (Dina Waters), house after a 26-hour shift, and on a high from the great news that she has been chosen as a hospital resident, Elizabeth is involved in a car accident.

Switch forward a couple months, lonely widowed architect David Abbott (Mark Ruffalo) no sooner moves into an apartment being temporarily subleased under mysterious circumstances that he is accosted by Elizabeth, who claims the place is her own. David initially thinks he's going crazy—she seems to show up randomly and abruptly, and he is the only one who can see her—and then starts to suspect she may be a ghost stuck in limbo. Once Elizabeth comes to term with the frightening idea that she may no longer be alive, they set out to investigate what happened to her after the auto accident. Meanwhile, romantic feelings arise, but how could a relationship possibly work for two people when one half of the couple may be dead and they can't even touch each other?

As a comedy, "Just Like Heaven" is sporadically amusing, but rarely of the laugh-out-loud variety. Much of the humor, stemming from Elizabeth entering David's body and making him look foolish in front of people, and the reactions David gets when it appears as if he's talking to thin air, has been played out so many times in past films that it feels rather stale. As a romance, the picture is deficient in sparks between Reese Witherspoon and Mark Ruffalo (2004's "13 Going on 30"), who work much better as friends than as a couple. Furthermore, it takes so long for the love story to take precipice over the story that, when it comes, the developments appear to be more of a requirement of the genre than a natural progression of two people's relationship. And as a supernatural tale involving a spirit and the only human being who can see and hear her, the movie doesn't take this plot hook seriously enough, instead using it as a mere gimmick to shield viewers from the truth that what they are watching is rigidly, sometimes embarrassingly, conventional.

Even as a fantasy-based entertainment, "Just Like Heaven" strains credibility the further it goes on. Screenwriters Peter Tolan (2005's "Guess Who") and Leslie Dixon (2003's "Freaky Friday") introduce several revelations that are supposed to be surprising, but are glaringly telegraphed far in advance. Worse, what happens in the last act is a cop-out, as they realize they've written themselves into a corner and do everything they can to make the ending as happy-go-lucky—and, thus, plainly ludicrous—as possible. The final scene leaves one smiling for all the wrong reasons; what is supposed to be swirlingly romantic is actually so unabashedly syrupy that an acre of maple trees must have been torn down in order to capture it on film.

Reese Witherspoon rises above the onslaught of sentimentality to form a complex character. Her Elizabeth, who spends most of the time in spirit form as she slowly remembers her past, is a young woman of depth and a lot of regrets, and Witherspoon slides with ease between the broad moments of comedy and the quieter moments of introspection. Elizabeth's realization that she spent so much time at work that she forgot to savor the rest of what her life had to offer is touching without being mawkish—the one dramatic element that actually works.

As David, Mark Ruffalo is fine, but his role is unremarkable; he has been so much better in the past that one suspects this was a part he took more for financial gain than creative passion. The supporting cast is clunkily integrated into the story and decidedly superfluous, with Jon Heder (2004's "Napoleon Dynamite") called upon to recite a bunch of unfunny one-liners as an alleged medium, and Ivana Milicevic (2003's "Paycheck") wasted as David's sexpot neighbor, Katrina. Katrina is promptly forgotten about after two scenes, both of which should have been left on the cutting room floor.

Based on the novel, "If Only It Were True," by Marc Levy, and named after the great '80s song by The Cure (which shows up via a cover version during the opening credits and the original recording at the end), "Just Like Heaven" is a lightweight diversion of minimal charm. For Witherspoon alone, the viewing experience isn't nearly as interminable as it could have been, and the pacing moves fast enough that the film doesn't wear out its welcome so much as it wears on one's suspension of how much mawkishness he or she can withstand. Still, "Just Like Heaven" squanders an intriguing premise that required a tougher, more substantial treatment to make it work. As is, the movie is consistently too dumb in its plotting to elicit the sort of enchantment and whimsy it strives for.