It's pretty much the "otherworldly girlfriend" version of the harem comedy. We've seen this about 87,000 times in other forms--Urusei Yatsura, Tenchi Muyo!, Oh! My Goddess!, among others--and this iteration is a good adaptation of the genre. The girls are cute and the fan service is pretty good. (The boobs are a bit too big.)
The tsundere'kko, Kirie, is--as they usually are--too violent and too ready to blame the main character, Yukinari, for everything. Despite that, I really like the character in her non-violent moments. Like all the female characters in the series, she has much larger-than-normal breasts. Someone mentions that she wears an F-cup and that it is suboptimal for displaying her figure--recall that a Japanese bra is one cup size smaller, so it would be an American DD-cup, which is big even for an American 17-year-old. (Not impossible. Just unlikely when she's so slender otherwise.)
I've never liked it when the main character is punished for things that are not his fault. I don't think it's funny; this kind of thing kept me from liking Urusei Yatsura for a long time. Kirie's primary riff is, "You saw a naked girl! You did it on purpose! You're a pervert!" ...and cue the violence. It gets tiring, and I have yet to see it done in a way I find funny.
But none of these issues detract from the entertainment value of the series. There are no groundbreaking developments or really new ideas in this series, but it's not a train wreck (at least as far as its first season) and I find myself wanting to watch it a second time.
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A note on diacritics:
I realize that 99.997% of people don't insert an apostrophe into "meganekko" and "tsunderekko". Those spellings are the commonly accepted ones, and it's not technically correct to insert the apostrophes, but I do it for a couple of reasons.
First, in Japanese, the characters which form the words make it obvious that "kko" means "girl".
Second, when reading the romaji version, my eyes tend to see "mega-nekko". (Some kind of giant cat? Maybe a giant cat mech?)
So I insert the apostrophe to indicate a point where pronunciation stops, which is one of the uses of that mark. Hence, "megane'kko" and "tsundere'kko". If we were all reading and writing Japanese it wouldn't be necessary; but since translation is always imperfect I figure I might as well make the imperfection fall on the side of readability.
From time to time I will do things like this, without warning, solely because it makes it easier for me to read what I write. (I learned fairly early on how and when a writer can bend and/or break the rules of grammar and punctuation, so I don't even feel remotely guilty over it. Ha, ha.)
As an SF writer I like to play around with diacritics, anyway.