Combat in 4e D&D allows players to take three actions on their turn: standard, move and minor. Different combinations of these actions are possible, but using these three actions are the basis for a round of combat.
Since the release of 4e many people have complained that combat is far too slow. The amount of options available and interupt powers just slow things down too much.
In a recent article Gamefiend from At-Will noted that “the speed of 4e is not a bug, rather it’s a feature.” I commend the full article to your attention (The Speed of Choice: the Real Reason your 4e Fights are so Damn Slow) as Gamefiend has hit on some very interesting points. Of course the speed of combat isn’t the true complaint that many have with 4e D&D. If this were the case the countless articles on speeding up combat that exist would be all that any gaming group would require.
However, the speed of combat isn’t the true issue with 4e D&D. Rather it is the cause of the issue which is a lack of time remaining to develop key role-playing opportunities. This is perhaps most prevalent in organized play where players only have four hours to finish an adventure, but it is also an issue for those playing with their home groups. If it takes approximately 10 encounters to gain a level and the average four hour session only has two or three combat encounters the pace of levelling and the game is very slow. If there is no room for role-playing in between combat encounters, D&D becomes more of a roll-playing game.
This is where the 4th action comes into play.