In a summer-movie season littered with speeding cruise liners and hijacked planes and stupid-looking, nipple-enhancing bat costumes, My Best Friend's Wedding is a marginally entertaining diversion; too bad it can't overcome a few central flaws. As the tale of Julia Roberts' quest to steal the love of best friend Dermot Mulroney from too-perfect Cameron Diaz unfolds, Wedding never compensates for the fact that Mulroney's character is an underwritten, blankly rendered pretty-boy: Roberts' performance is multifaceted enough to suggest a deep, complex relationship, but Mulroney never comes off as more than a sort of one-dimensional dope. Just as crippling is the movie's tendency to waver back and forth between black comedy and Nora Ephron-esque schmaltz. For every darkly comic scene, there's one in which Roberts stares into the distance while an oldie plays, or teen boys sing while comically under the influence of helium, or debutante caricatures engage in wacky mishaps. Amazingly, Wedding's scene-stealer is Rupert Everett, who turns the "gay friend" archetype into the movie's most likable character. He's the voice of reason, of course, but Everett's performance oozes genuine charisma. There are other things going for My Best Friend's Weddingincluding a suprisingly well-conceived endingbut it's hard to recommend a movie in which Julia Roberts falls down comically not once, not twice, not three times, not four times... Five times!