Yes, the premise sounds silly and leads to LOTS of fanservice (which in itself is never a bad thing) but as the series goes along a more serious story starts to develop.
While the ending did feel a bit flat (still needs to see the OAD) it is well worth the watch.
Breasts that are as big as the character`s head or possibly a bit bigger are still considered large; however, breasts that take at least as much space as the rest of the chest or the abdomen, or that are almost as big but have an absurdly unnatural shape, are the less common gigantic breasts instead.
Exposure is usually accidental, but may also be deliberate.
A comedy anime is laced with humour and sets out to provoke laughter from the audience.
Japanese humour can be a bit strange to westerners, so if you`re new to this type of humour, just bear with it; it`ll most likely grow on you if you`re a fan of other kinds of comedy.
Nudity is the state of wearing no clothing and exposing the bare skin or intimate parts.
Especially gratuitous fanservice shows tend to show their characters frequently without any clothes, though often hiding genitals through the means of additions like steam."Panties" in Japanese.