I think the unappealing factor isn't a visual one, but a content one. It blueballs you for what feels like 40 trillion years when Densuke and Chiharu are clearly masturbating to each other every night by episode 2. They never get together. A non-insignificant portion of the series pretends to be harem, but fucking nothing happens and it's the worst sort of status quo.
Let me break down an average Eiken plot for you:>Densuke does a thing>Circumstances (usually Kirika) involve Chiharu or Girl of the Week>Densuke has pantsu and/or boob in his face more times in 10 minutes than the collective of /a/ has had in their lifetime.>Episode ends and we pretend it never happened.>Rinse, Lather, Repeat.
That's fine when it's something like a 3-episode OVA, since you don't expect it to really go anywhere. When it's a manga/anime series with a staggering number of chapters and episodes, you wonder how the fuck the writer has managed to make so much Nothing.