Hi there,
I guess the thread title explains everything. I´m just curious as I began playing with AD&D 2nd edition but never knew how it differs from 1st edition AD&D. Also, would you say that 2nd edition improved the game?
If you focus on just the original rule books, 1E was Gary Gygax collecting a lot of house-rules for OD&D and placing them into a single place. It's more brilliant because he included everything (also has more weaker material). In my opinion of how to play 1E, the trick is to take what you like and ignore what you do not (boot hill rules may not be for everyone, 100 types of polearms was likely overkill). Balance seemed based on the idea that characters progress slowly and mortality among adventurers is very high.
This began the tradition of every table doing the game slightly different -- a fun phenomenon that I saw a lot of in the late 80's.
In 2E they tried to make a more systematic game. It takes a lot less vetting to work and incorporates some of the good ideas of later 1E. It was also deliberating designed with 1E to work with so many rough patches are fixed. It removes a lot of the fun advice and general game philosophy of the 1E DMG (although some comes back in splatbooks).
It had different issues, in the end. I disliked the art of the 2.5E PHB with an undying passion which likely biases me somewhat and I found the sphere approach with clerics needlessly complicated (little did I know). But a lot of material was added to the PHB to make it less necessary for everyone to own a DMG.
I liked both, a lot.