I got the original AFF (Advanced Fighting Fantasy) books (Dungeoneer, Blacksand, and Allansia) after I got AFF2e (Arion Games's Advanced Fighting Fantasy, Second Edition), intending to compare them by reading them and playing them both, along with the original FF:TIRpG (Fighting Fantasy: The Introductory Role-playing Game). This has gone a lot slower than I intended, but I have played several sessions of FF:TIRpG, and have been rereading and comparing AFF and AFF2e recently, in preparation for playing AFF.
It looks like AFF2e has been adjusted to make play more consistent, balanced, and suitable for long-term play. Starting attributes are point-buy instead of random, and the values for SKILL, STAMINA, and LUCK have lower ranges — 4–7, 8–16, and 4–7 vs. the original 7–12, 14–24, and 7–12. There's been some addition of detail — random Armor rolls — and some other tweaking — weapon damages are higher.
AFF2e gains a lot from being presented in one book, and integrating the Sorcery! magic system, but there are some places where it is not explained quite as well as it could be, and there are some typographical oddities, the illustrations (most — perhaps all — from the original AFF?) are somewhat faded grey rather than the original black, and I'm not keen on the layout or fonts.
AFF definitely harkens back to the wilder, early days of RPGs, when balance was not so important, and the oracular powers of random dices were used more.
Organizationally AFF suffers from being presented in three books as it makes reference harder, but pedagogically it may gain — there's a smaller amount to be learned at once, and it's playable with just the first book. The books' smaller physical dimensions make them easier to hold and read, and the layout is simple and suitable for this size book. I think the books generally explain things more clearly, and I like the movie/TV series metaphor it uses, and the tone of the writing is a bit more engaging. And it includes two the mass combat systems.
One thing about the system as a whole will be an advantage to some and a disadvantage to others is that the system is very simple. AFF2e adds a few simple tactical options, but even so the combat system has little detail, while in the original AFF there's little besides a normal attack or a dodge. Those who enjoy system complexity and system tactical detail in their systems may find AFF and AFF2e lacking, but those who prefer simple systems will find the combats easy and be glad to get back to the role-playing.