I would never have suggested this before playing 4e, but this is actually an area where the whole battlemat and minis thing pays off in conjunction with the rules. Basically, the game quite profoundly rewards staying in motion, and makes it easy to do so, and the net result is that you never (well, rarely) reach the point in combat where two people are standing perfectly still beating on each other. It's specific to combat, but it keeps changing up the decision making process. That constant change of situation is definitely a trick to keep things fresh.