It seemed like in classic there were all kinds of hidden tricks, and bugs to exploit. Most of which were pretty harmless.
However the best players knew all the tricks and used them to their advantage. If you wanted to do some of the top tier content you essentially were required to know tons of little tricks to min/max the game.
Now everything is super streamline, no tricks, everything is documented. But the game is a little less fun. Instead of finding fun, we now have to be handed it. Plus the game is orders of magnitude easier... When was the last time you died in a 5 man?