I get the MonMusu comparisons, but I still don't agree with them. It seems like there's a trend both series follow in the introduction of monster races, especially with a lamia as a main cast memeber alongside the MC, and Kanemaki Thomas has done some work for the MonMusu anthologies in the past. They're way different beyond that, though. Oishasan feels like there's more depth to it, the chronology is a bit more established, and visually completely different, not to mention a wildly different setting.
I'm mostly just here to ramble about the artist.
I absolutely adore Kanemaki Thomas' visual style, and have for a long time, so I'm a bit biased. I just love seeing so much complex penwork all over the pages. So much of the background is still detailed, complex penwork that meshes so well with the foreground without clashing. His extensive use of sharp black inking alongside the linework and white space also amazes me every time I see it. Visually he doesn't try to go for photorealism, but Kanemaki still manages to do some wonderfully fleshed out, grounded art with a really charming style that I'm finally glad to see in a serialization with a larger audience and not in the niche of monster girl H-doujin.