Honestly, this is one of my favorite harems because the dynamic is strong and justified. Often times you get irritating comments like "beta MC" and the like, but it doesn't apply her because the one thing MC has going for him is his sheer willpower and determination, even if he is a complete dumbass both socially and intellectually.
Also, I like how the girls don't pull the "oh no we're all having this awkward misunderstanding" bullshit. Whenever it happens, it's in MC's head most of the time, and the sister have to pull him back into reality and snap him out of his guilty conscious. It's a clever inversion of the stereotypical hijinks, and makes the characters so much more interesting.
@Koni
But yeah, I mostly agree with that. I actually think it would be funny if the cycle continues and he gets a harem end without realizing it.