If you've seen a preview - or even a poster - for "Daddy's Home," you can imagine how the movie goes.

Will Ferrell is buttoned up, straight-laced and dutiful, a newlywed stepdad delighting in fatherhood. Mark Wahlberg is tough, edgy and mysterious, the birth father who disappeared. The film is about their battle for the kids' affection, dad versus stepdad (also the film's slogan).

Don't you just already know that, in the end, they'll do what's best for the kids? Of course you do. This is a Hollywood movie, after all.

So it's all about the journey, and writer-director Sean Anders ("Horrible Bosses 2") doesn't take his story or his stars beyond what's expected. It's the poster, or the trailer, for 96 minutes.

That's not to say it's all bad, especially if you like alpha-male puffery. Ferrell and Wahlberg may play familiar, predictable archetypes, but they're still charming, charismatic movie stars being ridiculous onscreen.

Ferrell is Brad Whitaker, a quiet, stable guy eight months into his marriage with Sarah (Linda Cardellini). He always wanted to be a dad, and he's excited about the relationship he's developing with her two young kids.

That fledgling bond is threatened by a surprise visit from Dusty Mayron (Wahlberg), Sarah's ex and the kids' biological father. Instantly, the dad-fight is on.

It's not clear how long Dusty has been gone, but it's obvious he's everything Brad is not. Brad works at a smooth-jazz radio station and cries every time one of his stepkids says something sweet. Dusty is muscular and freewheeling and hints that he's some kind of mercenary. Wahlberg does lots of shirtless pushups in the film.

The tough guy-nice guy dichotomy is a setup for various showdowns of stereotypical masculinity: building stuff, handling bullies, even penis size (seriously).

It could all be cute enough, but Brad is so naive as to be completely unbelievable. This grown man never once suspects a shred of insincerity or manipulation from a handsome and mysterious romantic rival? Hasn't he ever read a book or seen a movie? And if Brad is trying to win over his family with extravagant gifts like basketball playoff tickets, why would he buy a seat for Dusty?

Then there's the sexist subplot about virility and maternity. Brad is sterile, and even though Sarah is happy with her kids and her career, what she really wants is another baby - so much so that she giddily cheers and runs off to call her mother at the mere thought of the possibility. Thankfully, Dusty knows the best fertility doctor in town.

Ultimately, "Daddy's Home" has a sweet message about the challenges and rewards of fatherhood. It even advocates for dance-offs as a means of conflict resolution. It's pure silliness, but it would have benefited from a little more smarts.