Half of my games are EMs and I play them much more frequently than the solid states.
You have rule sets with EMs as well, and they are typically more straightforward, but more difficult to accomplish receiving an extra ball or a special.
If the rule is that you have to drop down all drops to light special, it seems simple. Actually completing this goal is another thing. And that is what gives the longevity. Also, just because you are able to do so once, doesn't mean that you'll be able to do so every time. And if you do? Make it steeper. Adjust the machine from liberal to conservative post positions. Make it a drain monster.
I enjoy a nice ramp as much as the next guy. However, I prefer EMs due to the pure gameplay. Your ball is rarely trapped for more than a second or two anywhere, unlike in DMD machines where you have to wait for animations or callouts to complete. The bells and chimes are both soothing and infuriating. (Why can't I just hit that rollover for 5000 points?) I love the melodious sounds more than a pulsing solid state thump or modern movie music.
Having multiple EMs tuned up and humming side by side is wonderful as well when you have folks over to play. Ding Ding Clang Smack Buzz.
There are certain layouts that I don't click with, just as with more modern games.
If you click with the game and had a chance to play it a bit, chances are that you won't get sick of it. But do your research and see what one typically goes for before plunking down money. If it is priced high, you probably don't have to jump on it right away. If it is fully working, think of what that means for you (in terms of cash), if you don't like getting your hands dirty. You will eventually have to adjust a switch or change a lamp, just like in a modern game.
One last thing: I've never had a problem with the ball moving too slow on an EM that I owned. At shows, where they may be moved from level, or there is low line power, yes. Mine move too fast for me, that's for sure!
P.S. Not to shamelessly self-promote, but you're the target audience for the podcast I just started about the appeal of EMs and bingos. Heavy on the bingo talk in the first 8 episodes, but the 9th I released last night gives some general info about 60s EMs. http://foramusmentonly.libsyn.com