Lesson Learned: Hard (combat) encounters are the best

Essence: Easy combat encounters (less then the level of the party) are almost always a waste of time. Players tend to notice real quick whether enemies are a real threat or not and they do not feel powerful or challenged if the defeat a group of enemies without any resistance.
Encounters of the same level or one level higher are good to prevent that a group gets frustrated after a very hard combat or if they have lost fight.
But the hard combats (two or three levels higher than the party level) are the fights the players keep talking about even after the encounter and that stick in the memory.

Details: Currently I am running the Pyramid of Shadows adventure with a group of 5 players. The adventure is for level 7-9 but since the group was already at level 8 when they entered the pyramid most combats are one level less or the same level as the level of party.
The first couple of encounters I ran as described in the book . But they were only fun if one of the players was missing (which often was the cleric). The combats became a kind of routine and after we were finished playing the talk about the game was short if any took place at all.
Only when I started adapting the encounters and made them hard it felt as if the group became alive again. The players stayed more focused during the game and they time we talked after the game became longer. And believe me nothing gets you the attention of the player more then reducing the hp of his character to zero or bellow.
From all the encounters we had in the last 1 1/2 years I only can remember the really hard once.


Advice: Keep track of the healing surges the characters still have. If one ore more characters only have few surges left be weary with hard encounters. You want the encounters to challenging but not deadly.
Adapting encounters in D&D 4E is really easy. If I do not find the time to adapt the combats before the session I add another monster or so on the fly. But that often does not make the combat challenging enough. Currently my preferred way is to take the monsters as described in the adventures and increase the level with the help of the Monster Builder which takes me about 5min per encounter.