... to be fair to monster musume, at least basing it off the manga, I could actually see a scenario where rating it a 7.5/10 would be appropriate. Namely, relative to other works in its niche.
Yes, it's fanservice pandering harem drivel, and objectively pretty sub-par, but as fanservice pandering harem drivel goes, it's arguably one of the higher quality examples of it. Characters may be relatively derivative, but they're not entirely flat (even including the male!), there's some degree of character development, and character interactions aren't entirely static, the world-building isn't completely ignored (even if it by and large is drawing from porn scenarios, as befits its roots) and impacts the plot meaningfully (to the extent there is a plot in this genre of media, anyway), and the actual point of the work, the titillation, is pretty clean in terms of quality (if not content, ha) and handled comparatively tastefully and organically compared to a lot of the material in the field. It's not actually something you can charitably call "a bog standard by-the-books harem anime that just happens to have monster girls in it". Unless you haven't actually been exposed to many by-the-books harem animes, I guess.
As its particular sort of very soft softcore porn goes, I could see rating it a 6 or 7 on a ten point scale. It's not even remotely innovative or impressive, but it does what it's intending to do pretty competently, particularly relative to its compatriots. Damning with faint praise it may be, but the thing actually has a fair degree of merit. Not enough to save it from being drivel, but enough to elevate it close to the greatest heights drivel achieves. It would just deserve a three or four point knockoff if you were going to compare it to most anything outside its particular niche, heh.