Like others have said, the first half of this anime was much like the whole first season. Silly tone, guns-galore fanservice, and a general light-hearted disposition and attitude. During the third quarter, the tone shifted to being High-School DxD-esque, mixing ecchi with a somewhat serious story. Then, on the last quarter, it shifted even further, to the point it almost became a tragedy, with no ecchi involved and a miserable outcome. I see why the writers took the step, as they surely wanted to expand into non-ecchi territory in order to cater to a wider audience, which is perfectly okay, but in this case, as the original tone was so drastically different, the resulting tonal disonance makes the anime feel awkward in its presentation as a whole. Production-wise, voice acting and animation were moderately good, pretty much the same as the first season.
All in all, a peculiar shift in tone. Recommended for fans of the genre.