I didn't expect Yuusha-tachi (or let's just call it "The Heroes") to be great, since it's just a one-shot. But that's okay. You do not read The Heroes for the plot, you read it for best girl. Best girl is a cute bunny-looking adventurer.
The story's about animals, fighting against darkness. Yep, it sounds bad, which it is - for the most part. At least it had some good elements, too, like some of the scenes were a critic to society. But as I mentioned before: you don't read it for the plot - you read it for best girl.
The art is definitely the point where it shines the most, but it's by Inio Asano, so I already was expecting some superb art. The background was really well drawn, maybe that's one reason why it took me so long to get through the ~20 pages. I found myself not caring about anything, but the background. Just starring at it, doing nothing. But hey, I did the same thing with best girl, you just can not stop looking at her. I mean, come on, you can't deny she is one of the cutest things you have ever seen.
Since we're already there, let's talk about the character design.
It was something unique - something you don't see often. Ofc this could mean it's bad, too, since being unique isn't all it takes to be "good". But well, I liked it. I thought Asano did a great job there (especially with best girl).
The atmosphere was something I found to be really good. To be honest, I would contuine reading this Manga just for the atmosphere (and for best girl, of course).
In the end I'd say, that "The Heroes" is something you can read for the art, the atmosphere and best girl; but if you're looking for something with a great plot, you should probably stay away from this.