Haruhi main strength is her impasse and many fans love to see her on this constant state of impasse. Once she resolved or move forward in her life, it will not be "Melancholy of Suzumiya Haruhi". Her total obliviousness to human emotions also adds to the appeal too for most people.
That is why some people disliked the anime despite the appeal, it did not really progressed in terms of character development. You can say most of anime fans are self indulgent and Haruhi hits on that spot so it becomes the hottest anime around. The self indulgence flag is proudly hoisted by Haruhi and SOS Brigade like the Marines in Iwojima Mount Suribachi.
That is how I see it.
The review on this anime soon.
