i wouldn't necessarily chalk up people struggling to make it through this book as having a short attention span. granted i have only read the fountainhead, but i am pretty sure that will always be [more than] enough. i understand rand has certain philosophies she wishes to expound. i think there is no denying she has some interesting ideas, some of which are spot-on. not only could i deal with how cynical a view these philosophies present, i had/have similar views myself.
still, the main thing is making it through the novel, and if AS is anything like the fountainhead i'm sorry, but the writing is poor. having good ideas, being intelligent, and presenting it in an engaging manner can be mutually exclusive. in this case i would say that they are. the problem is, rand can't find a middle ground between telling a story and espousing her beliefs. instead we are given story with characters who act based on this belief system and yet are still given to long monologues outlining these beliefs. be subtle, or be blatant, but don't try to do both, especially when your novel turns out monstrously long.
i have read many long books and enjoyed most every word. i would not put the fountainhead on that list. i'm not going to argue about the quality of the writing anymore since that is subjective. as i said, i don't feel it is particularly well-written. i say read the cliff notes or a good analysis with excerpts if you want and spend more time on some british and russian classics (sorry horace mann and flaubert, the english translations were rough for me, maybe when i speak fluent french and german). all i'm saying is, not every that is a struggle (like finishing this book seems to be for you) is worth. but hey, this is all just my opinion.