I was first dissappointed when I saw the simple art style. It looks more like a slice of life OVA than a full fleshed movie. Just because it's short doesn't mean it has to lack quality, as we can for example see in Kotonoha no Niwa.
The Plot is much simpler than say The girl who leapt through time or Summer Wars - that would be expected from such a short span, especially if it goes into the peacefully paced slice of life genre.
Even the music didn't seem to have any theme you could remember.
However all that doesn't mean that it's not a movie I would recommend everyone to watch. The pace and feeling to it was perfect and an astonishing animation wasn't necessary - the idea to the plot was perfect enough to hit you right in your guts and let the feels stagger you even minutes later.
However it is quite sad that the music is so weak. I can overlook a simple animation but I think a brilliant soundtrack could have given it the chance to guide you through the movie a lot more smoothly and continuously spoken to emotions if that makes any sense.
All in all: weak animation and soundtrack but neat pace and a plot that everyone should have seen. Really enjoyable.