I enjoyed much of Brittany Runs A Marathon. We see Brittany's lifestyle and she's come to terms with her not being happy being overweight. So she looks for the cheapest way to drop pounds, and that's where the running comes in. As she starts her new hobby, she makes new friends along the way, and unfortunately has a falling out with her roommate. She also takes on a house or dog sitting job, but I can't recall what happened to her theater job she has initially in the movie.
The character of Brittany is a hard one to figure out. At first you think, oh poor her, I hope she does achieve her goal. But as time goes on, you see she's just as shallow and judgmental as the thin people she accused of being that towards her. And that's partly where the movie fails. We can't quite get emotionally invested in Brittany enough to root for her because she'll be nice one minute, but then turns around and is nasty the second.
Unfortunately the movie really drops the ball in the last act. We sort of see her making up to a bunch of friends she hurt, then the movie does this 1 year jump to the following year's marathon(?!). After the marathon we see that her life has changed somewhat. But the problem is that we don't see the progression to that change. I mean, she does still have a bond with those friends because they cheer her on, but is she a nicer person, is she still nasty? Did she ever make up with her former roommate? It just felt a bit rushed to show her as a completely different person, even though there was no real progression towards that as of the previous scenes.
Anyway, everyone in this movie is actually more likable than Brittany. Her FWB Jern is definitely a scene stealer, the actor playing him did a great job. A nice (rom?) com-ish film, even though the romance is kind of back-handed lol.