I read this because the zombie robot fish concept was so morbidly interesting to me. I'm relieved to see that this manga pretty much delivered on such creatures too. It started getting a bit too wacky for me to care towards the end, since the events become so outlandish (giant spider blimp-man, zombie circus, etc.).
Gyo's a cool read if you just want exactly what's on the tin, even if it doesn't offer much outside of it.