Bahahahahahahahahaha.
I really have no idea how you manage to hate the second half of SAO so much. It's not like it's even worse than the first half. I guess it's mostly just your inordinate hatred for Suguha and the very idea of incest talking (which I also can't really understand), but even so.
And the way you're deriding it here doesn't even make sense. When does the second half of SAO ever try to be "deep and subtle"? It's pretty goddamn straightforward if you ask me. Sure it has themes (mostly the same ones from the first half, like the validity of a virtual world as long as it's real to the people experiencing it) but for the most part it's just an incredibly straightforward rescue story with the most straightforwardly despicable villain you ever saw and a pretty standard romantic misunderstanding subplot running alongside. Just simple, honest fun.
Similarly, you seem to be under the twisted impression that the ALO arc was somehow trying to convince you that it's normal to have feelings for your sister, when it never did anything of the sort. The whole incest subplot started because of the confused feelings that resulted from their separate realisations that they weren't siblings, and even so Kirito himself never felt much of anything romantic towards Sugu at all. There may have been vague hints of possible attraction when he didn't know it was her, but even then he didn't really have eyes for anyone but Asuna. The romantic feelings were always a one-sided deal.
Thank you. I watched all the episodes in quick succession, and this is pretty much how I see it. There is no drop in quality in the second half, it's pretty consistent all the way through.
Now, if someone would just make a film adaptation of the Otherland series...