I'm on the fence with EMH. Extra hours are good, but they tend to be more crowded. Last November we were in Epcot for evening EMH and it was packed. In the two hours, we rode two rides (Soarin and Test Track of course).
For morning EMH, you need to be there at rope drop. If not, you will enter a crowded park. It's happened to us and it's disappointing. I asked myself, how could all these people be staying at a Disney hotel?
Overall, it's extra park time (crowded or not). So, that has got to be a good thing.