A soldier boy named John (Channing Tatum) and a student girl named Savannah (Amanda Seyfried) fall in love under a full South Carolina beach moon while he's on leave and she's on college break in Dear John. When John goes back to his army unit and Savannah goes back to her dorm, they write each other letters hence the title of this perfunctory weepie, a determinedly uninteresting, sanded-down, prettied-up adaptation of Nicholas Sparks' already taste-tested 2006 best selling novel of the same name. But since the phrase ''Dear John'' also traditionally refers to the kind of letter a girl writes a boy when she wants to break up with him, readers and non-readers alike won't be surprised when romantic heartbreak alters the course of this tremulous saga. Lasse Hallstrom (The Cider House Rules) directs with a softness that makes even combat look tranquil.
The subplot about autism is its own topical distraction, as it is in the book. So's cancer. You might think that's enough of an assortment plate of issues to work with, but the producers thought otherwise: This may be the rare adaptation of a mass-market best-seller that adds complications in, rather than cuts them out. As a result, screenwriter and coproducer Jamie Linden (We Are Marshall) is kept busy writing stilted speeches for John to deliver likening himself to a coin, minted in the U.S. Army. John's dad (Richard Jenkins), you see, collects coins.
In such an overworked project (with a premise-busting epilogue that appears to have been added at the last minute), Tatum (G.I. Joe) and Seyfried (Mamma Mia!) are all the more welcome. Fresh, comely, and unpretentious, they bring real warmth and believability to the early scenes of young love. Ironically, they make the bond between John and Savannah look so natural that the ''dear John'' turn in their relationship makes even less sense than it does in the book. But that, dear reader, is something to ask the author, not this weightless movie. C+