The story arc would be a good model for the series to follow if implemented correctly. Yet if every part of one girl's arc pans out in 4 short ep. this'll make the series feel rushed and you'll never get to connect with the characters on an emotion level, it'll be strictly superficial. Parts of the each of the arcs should be implemented in conjuncture with the other arcs when it makes sense in the overall progression of the story. This is sort of what Clannad did (in many respects it worked and in many respects it didn't). What is wrong with the current story structure is, now every arc in split into a short timeline of events that relate in no way to the protagonist's character development, and basically once your favorite character's arc is over the season ends (like the series could end now and I wouldn't be disappointed =3). This model would be better for a series of full length ova's imo. But it's still only 4 ep. in, so we'll see.
And IMHO, although the sex scene was a valuable continuity device, it was way too sleazy and a overly gratuitous effort, for what would seem a delicate and emotional moment...sure fan-service is great and all, but moderation is great too =/
