Route 20 is a manga about one kid who's in a biker gang, and the trouble he gets into along the way. The story is told in a somewhat haphazard way, with things changing left and right, but I feel like that works in it's favor, making the pacing of the manga feel similar to the life of chaos that the main character has chosen. It helps set the tone of the manga well. Each scene is also very nicely done, with interesting, cinematic-like storytelling.

The art is pretty nice, with lots of interesting character designs that are expressive and iconic. There are also some cool looking robot and futuristic car designs which help flesh out the world, and some backgrounds which are fairly nice looking, but perhaps a bit minimalist.
The art is detailed overall, but I also can't help but think it's a bit lacking in spots. Still, it looks good.

The characters end up becoming interesting and by the end, I felt like I wanted to see more of all of them. However, that's where we begin to get to the problems.
Despite liking the manga, by the end, I was left wanting more. Each chapter is very short, being only 8-15 pages long. In total, the manga is only about 60 pages long.
I think a short one-shot like this can be interesting when done right, but in this case the reader only begins to get introduced to the characters and the story, and despite very strong introductions to all of them, all of the sudden it's over, and you desperately just want to continue reading... but you can't.

Ultimately, this manga is a super quick romp through a very dense and interesting world, with nice looking art and interesting characters. However, it also doesn't go anywhere, and just kind of ends without much of a conclusion. Being as short as it is, it ends up feeling more like the first two episodes of a longer series, except there was never a continuation afterwards, making all of it's good parts seem disappointing, because they end up being wasted.