This film is worth the watch, but I'm still giving it a thumbs down.
In short, this is a movie about Sam. A seemingly good guy, collecting some belongings from his ex-girlfriend's apartment/flat while she has a party. While he's hidden himself away in room sorting through his property in what seems like a decision on what to keep or throw away, Sam falls asleep to awaken the next day to a full-on zombie apocalypse, and without a clear destination he can run to, chooses to remain in the apartment building he was in.
The movie, while well acted, missed a great opportunity for a "Flight Club" like reveal. In my opinion the director should have shortened the second act significantly, and expanded the 3rd act with "Sarah" proportionately. Not wanting to give any spoilers, but the reveal at the end of the 3rd act should have been more significant, while the 2nd act spends a significant amount of time on what's ultimately mundane housekeeping missions, such as cleaning the apartment of blood, the searching for food, and determining which apartments were occupied or not.
I was very disappointed in the 4th act. It felt rushed and implausible. Our protagonist should have had more obstacles to overcome in his escape. As well, the writers and directors can't seem to choose between slow walkers or frenzied runners. It's whatever seems to work better for a particular scene, and that's really apparent by the conclusion.
As I said, it's worth a watch, at the very least as background noise while doing chores, so you're not bogged down during the slower parts of the film. In the end, I do hope a talented team might take this film and remake it with a better balance with an emphasis on the changeover at the end of the 3rd act.