Reviewing "Diary of a Wimpy Kid" movies is becoming an annual task but with diminishing returns.

"Diary of a Wimpy Kid: Dog Days," the third feature in a series that began in 2010 and is based on novels by children's author Jeff Kinney, has a lot going for it. But it is less unified and more predictable than its predecessors, and doesn't play to all the franchise's earlier strengths.

On the other hand, the film ratchets up a couple of key relationships to good effect, and the best character in all three features, an attitude-challenged ne'er-do-well spiritedly played by Devon Bostick (star of Atom Egoyan's 2008 "Adoration"), deservedly steals the show.

Similar to the old Fred Savage television sitcom "The Wonder Years," the "Diary" movies star Zachary Gordon as young teen Greg Heffley, for whom there are no straight lines between desire and result. Attempting but failing to get a complete phone number from a pretty classmate, Holly (Peyton List), on the last day of school, Greg constructs an elaborate ruse to see her all summer at a country club to which he does not belong.

Because deception weaves a tangled web, in short order Greg is forced to lie about his identity, about his ineptitude playing tennis (Holly teaches the sport to little kids), about securing a summer job at the club and much else. As Greg digs his hole deeper, the film is supposed to get funnier. But by now — three movies in — Greg's issues with chronic dissembling feel creepy.

The best stuff in "Dog Days" are a few comic set pieces, but returning director David Bowers can't quite make them leap off the screen as he has before. Though Bostick (who has a memorable musical number), as brother Rodrick, gets an expanded role, and there's more to do than ever for Steve Zahn as Greg's well-meaning father, it's sad to see Rachael Harris lose her slightly weird edge as Greg's progressive mother, and truly unfortunate that most of the returning youngsters (including local actor Karan Brar) don't get to make another big impression.

Tom Keogh: tomwkeogh@gmail.com