Vince Vaughn is at a crossroads, and beyond whatever value it has as a piece of entertainment, "Delivery Man" is a fascinating snapshot of a star in flux, struggling to maintain a comic persona that he's outgrown. It's a perfect collision of actor and material, but maybe not for the most apparent reason.

David Wozniak is a train crash of a person and, in fine Hollywood fashion, he's somehow managed to remain a complete train crash well into his 40s. That's mainly because he works for his father as part of the family business, a butcher's shop, and they seem willing to cut him a fair amount of slack.

At some point, you age out of playing these roles or the films start to feel somewhat pathetic, and I think Vince Vaughn has just reached that particular moment. If David is a 30 year old character, this is a turning point. If he's a 40 year old character, this is a last chance. Desperation changes as characters age, and so the stakes in "Delivery Man" are fairly high for David. He's got a regular girlfriend who he's ended up disappointing and hurting so many times that things are imploding as the film opens, and Emma (Cobie Smulders) is ready to move on. Or she is until she learns that she's pregnant, suddenly making things between her and David more urgent. He's either got to snap into focus as a person, or she has to move on and build a safe life for her child.

You could probably make a solid and interesting character piece just dealing with that situation, especially in an age where the man-child archetype has become so omnipresent. "Delivery Man," based on the 2011 film "Starbuck" and directed by the same filmmaker, Ken Scott, has a huge wrinkle to throw in, though, since David once earned a ton of money by donating sperm to a sperm bank. Because of that, and because of a clerical error where his samples were for some reason the only ones being used, he learns that he is the biological father of over 500 children, and now many of them have gotten together to sue the fertility clinic so they can learn his identity. He's known only by the donor name, Starbuck, and he has to ask his best friend Brett (Chris Pratt) to defend him in the court case.

I can't imagine the legality of "Delivery Man" stands up to any serious scrutiny. For some reason, David is given a complete dossier on all 500-plus kids, many of whom are already adults, which sets up the film's main premise. As a parent, one of the things that is on your mind every second of the pregnancy is the question of who your child will be. My wife and I didn't want to know the gender of either of our kids before they were born, and that surprise made their births into these brilliant, beautiful moments of revelation for us. It also meant that for nine full months, I was constantly imagining the people they might become. In "Delivery Man," David gets a chance to see all the possible answers to that question played out. Could he have an NBA player or a drug addicted barista? Could he end up with a child so developmentally challenged that they can't live outside of an assisted-care facility or a daughter so hot that she stops traffic in her wake? When you're talking about almost 600 kids, you're talking about a full spectrum of possible outcomes to check in on and experience by proxy, giving literal physical shape to the anxieties of expectant parenthood. It's the sort of big idea that requires a deft touch, especially if you're mixing some fairly broad comedy with some fairly naked sentiment.

This sounds like the exact sort of vehicle where Vince Vaughn can break out his patented motormouth routine, but the film's biggest surprise is that he's gone the other direction entirely. He plays David as a guy who has disappointed everyone enough times that he knows he's out of chances. He's trapped in a permanent cringe, and it's a weird fit for Vaughn. It's distinctly possible that he's played arch and ironic so many times now that sincere no longer fits. It doesn't help that Chris Pratt steals every single second he's onscreen. He's got four kids in the film, and the portrait of chaotic family life painted during his scenes is more interesting and entertaining than the rest of the movie. Pratt also knows how to find both the humor and the heart in a line and really sell both, and he almost feels like the evolution of a particular type of comic persona, with Vaughn further back along the developmental timeline. With Vaughn, "sweet" never quite fits properly, and it makes it hard to swallow some of the beats in the film as genuine. WIth Pratt, there's a sweetness that is innate, and it makes him compelling in a way that Vaughn can't quite manage.

I'm not sure why Ken Scott wanted to make the same film twice, but the result is both more polished than the original and more surface-level. If this is his audition to make big slick Hollywood comedies, then mission accomplished. It looks and plays the way it should, and he did a good job filling out the ensemble around Vaughn. Some of the younger cast playing his kids are good, but they don't really get a chance to register as full characters because there are so many of them. The whole thing has an amiable quality that makes it easy to watch, but it doesn't stick, and considering how serious some of the subject matter is, it should matter more. It should land harder.

This is one of those reviews that is hard to write precisely because I neither love nor hate the movie. It is a middling effort overall, and for Vaughn, it looks like he's finally reached the point where even he knows that he can't play this character forever. Once David makes that choice, he's ready to have a family of his own and commit as a husband and a father. Now that Vaughn's making that choice, I'm not sure what the next movie is, and it feels like he doesn't either.

"Delivery Man" opens in theaters everywhere tomorrow.