I used emulation to show a bunch of old PS1, PS2, and original Xbox games I had when I was younger to my partner. It was a fun evening, and they actually enjoyed most of them. They didn't really get into gaming until the Wii, so it was nice to see their reactions to some of the older stuff.
But I agree with the other comments here, it should really only be used for preservation or things you can't purchase from retail anymore.
I remember being blown away by a gameplay demo of Bioshock during E3. They used a lightning bolt to shock the water, and it worked?!
I rented the game for the Xbox 360, and was equally blown away by its story. What an awesome experience. I play though it occasionally on my PC just to live in its world again, though I think I like the original more than the remaster.