This movie was clearly made on zero budget, as akin to the previous similar zombie effort of Colin, as such you have to consider this and appreciate how much of a movie this actually turned out to be.
There is tension and compelling action, and the whole thing doesn't feel like filer, despite most of it taking place in a couple of small locations. The narration can get annoying but you can see that it is what stitches the filmed scenes together and is necessary. The effects mainly rely on editing and imagination, but again with no budget this makes sense. Generally the editing and directing are what make this any good. The only flaw is the writing, it is quite simplistic and the point of 'survival vs fighting back' is repeated over and over again despite the filmmakers message becoming clear about a third of the way into the movie.
Overall this isn't a bad effort considering the clear lack of budget, there have been a lot worse zombie movies made with a lot more to work with, so definitely worth a watch if you are looking to make something for nothing yourself.