1 Oh, Haruhi. On the one end of the spectrum you had Endless Eight. On the other... Disappearance, a film that only makes sense in context and is useless to the newcomer, but that doesn't matter because it's superbly well-done.
I'm very "over" the Haruhi thing nowadays but I have fond memories of some of it, at least.

2 Never watched any of it, but apparently there are people who make watching this an annual thing.

3 The Haruhi anime properties by KyoAni are modern landmarks, moreso than I think they're given credit for. The two anime series deserve credit for experimental filmmaking. They also were produced right as KyoAni was really upping the standard for quality art and anime, from "these guys are pretty good" to "the benchmark for tv series production". The sourced material deserves some credit for the storytelling, at least to the extent of providing and setting that made all this possible; but I have to admit I find the English translations to be rather pedestrian reading. It's possible the books read better in Japanese, as you can load more levels of subtle meaning in sentence structure and the use of various kanji and kana.

4

Beg to disagree.  I find the first season to be entertaining enough, but the second season was very much a monotonous bore (Something that the English VAs discovered to their dismay.).  However, KyoAni's experimental production actually decreased my enjoyment of the series, and represents the classic 'Just because it is different does not mean it is good' - which was something that was apparent to me back when fans were gushing over how great Season 1 was (IIRC, one guy on AnimeTV actually called it the greatest series of the decade.).  The original light novels were about as readable as Monogatari, and after a while, less interesting.  I would prefer reading anything by Kinoko Nasu than have to read Haruhi again...Though at least it is better than the works written by Kazuma Kamachi.

In terms of production quality, I would agree that KyoAni did an excellent job, but I always found to their anime to be just a hair under the best, even at their best.  There never seem to be enough difference in the quality to stand-out against, say, anime from A-1, assuming equal budgets.