I would not come into this manga with the same expectations that one has with the series. It is just a prototype, so it has a lot of flaws.
There is nothing amazing about the story. It gives background information on the world, as most oneshots set up, and focuses on the relationship between master and pupil and, of course, fighting titans. What I like about the story and setting, however, was seeing how the series originally started and what changes the mangaka made. For example, originally the walls were just really large trees instead of what they are in the manga; seeing small changes like
that make it worth the read.
The quality of art is mainly a subjective opinion, but at least for clarity, it is not fantastic. Isayama Hajime even wrote a note that said, "This is a work that I drew when I didn't know how to use a pen correctly and couldn't draw well". He definitely improved for the series. Don't come here expecting deep characters, either. There is a little development but not much.
Through all of this, I did enjoy the oneshot. Seeing how Shingeki no Kyojin originally started out was my main enjoyment, comparing this to what it is now. I would recommend this to anyone who has read the manga or seen the anime, just to at least understand where its origins lie. Even though this is the very beginning, anyone who has not started the series should read/watch it first and come to this last.