Combat in d&d frustrates me. Coming from a board game background, the combat system plays out like a really poorly designed war game.
I feel like the answer could go one of two ways.
1) simplify it down more so that it resolves faster. Right now it is very slow without many really interesting choices for most classes, yet it lingers. (I actually think this is the right option)
2) Actually design an interesting combat system that puts more weight on tactics and less weight on d20s