Hopeless romantics beware: "(500) Days of Summer" will not reaffirm your belief in eternal love. Or maybe it will. I saw it four days ago, and I still can't decide.

The new film recounts the year-and-a-half-long, on-again/off-again relationship between Tom (Joseph Gordon Levitt), an aspiring architect-turned-greeting card writer, and Summer (Zooey Deschanel), the new girl in the office. But as that booming narrator told you in the trailer released months ago (see it after the jump) and again reminds you during the title sequence, this is not a love story. In fact, this is the most unlikely of romantic comedies, the kind in which the girl tells the boy from the get-go that she doesn't believe in love, that she just wants to be friends, that she's not looking for anything serious. And means it. Really means it.

"(500) Days" unfolds in fits and starts, reversing and doubling back in a flash, just like the couple's relationship. In an early scene, Tom first spots Summer as she walks into a meeting to deliver her new boss a message; a few minutes later we're hundreds of days into the future -- notated with a constantly spinning on-screen relationship odometer -- and she wants to break up. Then we're suddenly back in an elevator in those first few days, Summer telling Tom she too loves the '80s British rock band The Smiths. For Tom, a burgeoning interest is suddenly love at first musical confession.

That's not exactly an overstatement. Much is made of the fact -- chiefly by Tom -- that the two seem utterly compatible: they both love karaoke and movies and frolicking in Ikea, and, yes, The Smiths. But is that enough? What if an unmistakable chemistry and even great sex are doused on those compatibility flames: is that enough fuel for a long-lasting relationship? Does all that add up to love, especially if one of the principle players doesn't believe in love in the first place?

It turns out it depends who you ask and on what day you ask, and that's half the fun and frustration of "(500) Days," fitting since this is a relationship that is both fun and frustrating. Levitt ("Third Rock from the Sun," "Brick," "Manic") and Deschanel ("Almost Famous," "Gigantic," "Manic") are perfect in these roles; Levitt's boy-next-door sweetness is never cloying, while Deschanel brings a sizable dose of humanity, logic, and yes, beauty, to her off-beat, odd-girl behavior. They work so well together because you want them to end up together, and yet know, deep down, this is not a love story.

The screenwriters, Scott Neustadter and Michael H. Weber, and director, Marc Webb, are strutting their stuff, too. The script is sharp and witty, but not overwhelming quirky. Woody Allen's "Annie Hall" is an obvious influence: "(500) Days" is a similar grab bag of cinematic tricks. There's that narrator and spinning day counter, plus Super 8 home videos; a musical number complete with chirping, animated blue bird; a scene that devolves into one of Tom's black-and-white sketches of Los Angeles; even a split screen of a party thrown by Summer: Tom's expectations of the proceedings on the left, what really happens on the right. (I half expected Annie Hall's uninterested, cigarette-smoking, mid-sex shade to walk passed in that last one.) An excellent soundtrack and Tom's funny best friends (and kid sister) help propel the story forward.

But are you going to like where the story ends up, even if you love the journey? Again, it depends on your degree of hopeless romanticism. The last scene, and particularly the excellent last line, bring Tom back to square one and day one, and you only hope that the next 500 days turn out different -- and perhaps even better -- than the last.