My biggest complaint regarding 4th edition, and really everything since 2nd Advanced, is that the game has become bloated with complexity. Once upon a time, D&D was the kind of game you could give your 10 year old kid and they could play on their own in a matter of minutes. I'd kind of like to move back towards that both for nostalgia's sake and for ease of play. I don't want to reinvent the wheel though. Here are some ideas I've had to patch the existing game.
1. The DM's word is law
This is a fairly common idea, but with the glut of rules it's easy to be a rules lawyer. I think we need to emphasize that the DM can suspend or alter any rule he or she chooses at any time. Similarly, the DM can make up a rule on the fly for any situation that isn't immediately familiar for expediency without bothering to reference a rule book.
2. One defense
Multiple defenses trip up my older players a lot. It makes sense to divide up the defenses into the different areas, but I think it can be more simply handled without breaking the game. I think all defenses can aggregate down to AC with modifiers based on role to account for the different nature of some attacks. For example, magic users would get a +2 versus spells and other magical effects, and clerics would get a +2 versus undead and mind altering effects.
3. No opportunity actions
I like the idea behind opportunity actions. However, they too trip up my older players and confuse my new people. They also don't interfere with movement as much as they probably are intended to. I'd just as soon do away with them. This is a problematic idea with 4e though because opportunity actions and interrupts in general are so common. Removing them practically requires a full rewrite of any Defender class and many other powers. Perhaps instead of granting opportunity attacks, immediate interrupts can be folded into a general bonus to damage against offending targets. I'll have to think on this a bit more.
4. Halve powers
Too many special powers paralyzes my players. I think they'd be just as happy with fewer options in play if they continued to have them outside of play. I appreciate the situational options of having multiple at-wills, but at the same time I think it would demand greater creativity from my players to use their common abilities and skills instead. I'd have most characters limited to one at-will, one encounter, and one daily power to start and probably have them swap out old powers for new ones instead of gaining more as they level up. I'd still want wizards still get more because it's kind of their thing, but even they would have fewer available powers in any given encounter.
5. No feats, backgrounds, or themes
Feats are a useful way to tailor a character's abilities, but they're also an unnecessary layer of complexity. I'd remove them entirely for the sake of expediting character generation. Likewise no Backgrounds or Themes. These increase the variables of character generation to offer players mechanical means of reflecting their background stories. I don't think that's necessary. A conversation with the DM should be enough to secure some small bonus in specific situations based on a background element.
Just to recap, applying these five changes would reduce character generation to selecting a stat array, applying racial modifications, selecting a class, and choosing powers, then equipment. That's still a couple more steps than I'd like. Maybe switching to a single stat array and using equipiment packages based on role would speed things up further. The changes would streamline combat down to all attacks going against one defense, reducing confusion and speeding up the pace. Without opportunity actions to trip things up, the only way players could interrupt the normal course of a round would be to declare a contingent action and hold.
Obviously, applying any changes will cause problems to present themselves. 4e is a carefully crafted tower and pulling parts out is likely to make it wobble a bit. Any other suggestions?