This is a point that I read on Alex Schroeder's blog (link):
"Rare Healing: Players need to avoid wandering monsters and avoid unnecessary fighting. This makes strategic decisions (when to fight) more important than tactical decisions (how to fight)."
I've never been able to put my finger on the thing in 4E that troublels me so much. But Alex hit the nail on the head: "Healing"
In 4E you get a bunch of "surges" which are in essence a mechanic that allows characters to "recharge" from encounter to encounter in order to keep the pace. Now, while this might not sound bad, it is a distinct deviation from older editions of play.
It is MUCH more tactical in play than strategic. Due to this difference, the focus of the game shifts from adventuring (older strategic based game) and trying to get from point A to point B without using up your super vital resources, to encounter to encounter type play and worrying about resources that "refresh".
I know I've read this before and that this is certainly not a new observation. But for some reason Alex's post just suddenly jumped out at me and I hit the "Ah Ha!" moment.