To OP, I would definitely put at least one EM in your line up and give it a little time. Don't get bored and bail...your feeling about the game will change if you grab a decent EM. Unfortunately, there are quite a few bad ones out there (sounds, play quality, etc.) Like others have said, do your research first, and play a few to see which you like before buying.
I always try to keep at least one (or two, or three, or four) EM's in my collection. Even when playing my BF, BH, BSD, POTO or other games I've had in the past, I love jumping onto an EM to "take a break." As many other posters have said, the rule set is often simplistic on an EM, but very challenging to accomplish. It's nice sometimes to get 10 points off a pop bumper hit, instead of 10 million.
I would recommend a Gottlieb wedgehead. Even a player's condition game has excellent chimes, and these are amongst the smoothest playing EM's you will ever come across. Even when I'm pounding my DMD and SS games, I'll jump onto my Sure Shot for a quick game or two (or three). The goal - hit all the rollovers to light the rack of billiard balls in the center of the PF. Trust me...on this game, more difficult than it sounds. Mindless fun. I also have a cherry Bally Hokus Pokus, which is excellent to play. Three spinners that you can hit all day, easy rule set, and one of the better Bally EM games (chimes, colors, layout, etc.).
Give an EM a chance. One in your collection is always good for the older crowd or relatives when they come over also. That was what they grew up with, and they often don't want to be bothered with newer games with complicated, deeper rule sets.