good point - I think making monsters easier to run in 4E has allowed me, as DM, to work more on the story in-game, creating better NPC personalities, etc. In my previous campaign, I spent so much time building encounters that I had no spare time to give the NPCs a personality and do more than loosely string the encounters together.
What rule system did you use for your previous campaign? I'm going to take a wild guess and say it was 3.5.
In 3.5 it was also easy to create monsters because each monster manual had the template already done for you.
Changing things around on the various monsters didn't take very long.