Most of the suggestions so far seem to want to move the game even further from its roots. So, to counter a few:
- have a reasonable selection of core classes (maybe 10-20) and get rid of prestige classes entirely;
- ban or severely restrict multiclassing (the idea here is to use the rules to emphasize that each character is an essential *part* of the team but can't do everything);
- empasize character personality over numbers - take as much of the "character build" concept out as possible;
- decide whether it's a medieval-based fantasy game or not, and if it is then play up the stereotypes (and if it isn't then decide what it *is*);
- eliminate most buffs, and make things that change base stats much less common overall;
- streamline and combine skills;
- cut the number of feats drastically and make some staple ones straight class abilities instead;
- bring back something like 1e's matrix table for turning undead, as the current system doesn't seem to work very well;
- make Illusionist and Necromancer their own classes and do away with other arcane schools of magic (while you're at it, make illusions affect touch again so an Illusionist can actually do something other than support);
- keep the divne-arcane split;
- back off on balance a bit...accept the fact that not all characters are created equal and that a well-played character with a memorable personality contributes far more to the game than a maxed-out automaton, regardless of its numbers;
- look to other games and editions for ideas that worked...1e's system shock mechanic, for example, or Star Wars' wound-vitality hit points system...and adopt them;
- have two side-by-side rule sets for level advancement - a fast-advance (for short campaigns of 1-2 years) and a slow-advance (for long campaigns of 5+ years);
- assume your target audience has some intelligence and don't need things to be dumbed down - we *are* capable of doing basic math (well, usually), geometry, physics, etc.;
- put more restrictions in the rules rather than less, with notes for if a DM wants to remove them, as it is far easier for a DM to remove a restriction than to impose one;
- do *not* go metric;
- keep the game playable without need to go anywhere near a computer;
- use % tables more often, they allow far more flexibility than a simple d20;
- give the game back the odd sense of humour it had in 1e...the ultra-basic artwork, the flowery Gygaxian turns of phrase, and so on.
How's that for a start?
Lanefan