1E/2E's negative ACs helped me tremendously get through algebra class, so I somewhat have a fondness for THAC0. However, keeping things straight like cursed Chain Mail -1 raising your AC (from 5 to 6) vs. Chain Mail +1, which lowered your AC (from 5 to 4), drove some of my players nuts.
Overall, I wouldn't mind going back to 2E, but I abhor (or more appropriately chafe against) 1E's restrictions. One of the things that really shone for our group were the class kits, and I loved the "Complete" books (well, maybe not Complete Elves, but I did allow it, begrudgingly). If there was an area that fell flat, it was 2E's adventure support.
(I was also quite happy when the demons and devils were taken out of the game during 2E - I was never fond of them, and being in the bible belt, not having them in the books made it easier to take the game a lot of places without disapproving looks or speeches).