I hate movies that are fundamentally flawed. There are some films whose entire foundation can be completely destroyed by a single intelligent thought. For example, I was at least a little disappointed when I realized that all of Star Wars could have been avoided if the rebels had merely found some other way to transmit the Death Star plans than having to physically carry them from one place to another, but I'm willing to overlook that because it's a great film despite its (admittedly numerous) flaws. But The Five-Year Engagement provides nothing to recover from its tragically senseless premise.
Tom (Jason Segel) first met Violet (Emily Blunt) at a New Year's Eve costume party, where he was dressed as a bunny and she as Princess Diana. There was an instant connection and their romance grew over the year, and the next New Year's Eve found them engaged. As they began planning their wedding, Violet was disappointed to learn that she did not get into the post-doctorate research program she'd applied to at UC Berkeley, but she was accepted into a similar program at the University of Michigan. Although he was horrified at the prospect of giving up his job as a chef at a prestigious San Francisco restaurant, he was outwardly supportive and didn't show a moment's hesitation at moving halfway across the country to support his soon-to-be wife.
For some reason that goes completely unexplained in the film, Tom and Violet are unable to get married before they leave, and they apparently don't realize that people can also get married in Michigan. So they put on their mopey faces and put off their wedding for two years, until Violet's program has ended and they can return to civilization. Because it seems that all Michiganians are completely devoid of culture, the best job Tom can find is making sandwiches at a deli, but he'll hold out for two years for his beloved. But when Violet's program is extended for another couple of years, the strength of their relationship begins to be tested.
The trailer for this movie made it seem like Tom and Violet would be separated for the duration of the engagement. If that had been the case, then their angst would have been justified and understandable, but because they are together the whole time, the entire premise of the film is completely demolished. There is absolutely no explanation for why they couldn't just get married in Michigan (or in San Francisco before they left, or over any of the summers between the spring and fall semesters), and because they're living together anyway and doing the kinds of things that married people do there's no explanation for the sense of urgency they feel to tie the knot.
The movie is over two hours long and very slowly paced, so it feels almost as if you're experiencing their five year engagement in real time. What little comedy there is has been spoiled by the trailer, so you're left with a couple of hours of two whiny people who are frustrated with each other and the "horrible" circumstances in which they find themselves. The filmmakers even managed to completely waste their casting of Alison Brie as Violet's sister and Jacki Weaver as her mother, and the bit parts for Mindy Kaling, Kevin Hart, Chris Parnell, and Molly Shannon are similarly squandered. Only Brian Posehn (in the role of Tom's coworker at the deli) brings any degree of fun to the film outside of the main characters, but that's far from enough to keep the film interesting.