It's a pretty good show. I was initially worried there would be a lot of random nonsensical stuff happening for "muh artistic value" but a lot of the absurd or mysterious stuff in the beginning actually begins to be explained later on. The characters have backstories, motivations, and feelings motivating their actions.
Don't let the MC put you off from watching this. As far as I know, being deaf and mute doesn't make you mentally retarded but the MC very much is. 90% of his personality is "feel sorry for me because I'm a cute dumb disabled baby" (even though his younger brother is reasonably intelligent). Yes, sometimes he has moments of normal-human-level cognition, but it's too rare.
Overall it has good art, a well-paced plot that makes sense, and fleshed-out characters. Would recommend.