Here is a hypthetical exercise in regards to things like balance, class design and things like that for D&DN.
It is your job to fix AD&D in whatever manor you see fit. You have to identify any problems with the game and then fix them in whatever way you see fit. The only thing is that the game has to be recognisable as AD&D and you have to assume AD&D fans would actually buy it so adding laser guns and spaceships is probably not a good idea. Pretend you are designing AD&D 3rd ed and pick up where 2nd ed left off or if you prefer you are designing AD&D 2nd ed back in 1987. Just specify which one you are using. Also decide on the scale of the changes.
1. Minor Changes. Tweak some numbers here and there or change some rules like level limits maybe racial restrictions things like that.
2. Major changes. Adding d20 mechanics, turning saves into Fort/Ref/Will or something else, rebuilding the classes from scratch etc. Still can't be to massive though as the game has to at least resemble AD&D so do not turn it into 3rd or 4th ed.
Fear is the Mind Killer