Why should you play first edition AD&D? Well its simple, its a wonderfully crafted game that has just enough balance between combat and roleplay with out all the annoying options the later editions give you to confuse you.
DON'T GET ME WRONG. There is nothing wrong with the later editions of the game, but as the game grew, there was more and more options added to the game, which made it confusing at times, making people have to flip to books constantly or re-read certain things to see how they worked in game... THIS SLOWED THE GAME DOWN.
I am not a man who likes to stick to the books, and I will make a on the fly judgement call just to keep the fun and excitement. There is not more annoying then, playing and getting into combat or social situation that requires a roll and having everyone argue about how something works... which has everyone flip to the books, find it and have to prove a point.
So to close this annoying rant, try out AD&D 1e, its simple, its easy and its fun!