My take-
I am a little older than the OP but only maybe 5-7 years or so. I recently finished resorting an EM machine kinda out of the blue impulse- wouldn't it be cool to try it sorta thing. I probably played a few EM in arcades when I was young but mostly had played SS. I have to say, the EM machines to me are the "true" pinball machine in that they are the first recognizable pinball machines if you look at it from purely a mechanical whats on the board and how does it work together kind of perspective.
I have now been playing my machine for about 2-3 months with friends on the weekends and very occasionally on a evening when I have 10 minutes. Here is what I am starting to find.
I have a super spin Gottlieb 1977 machine that has been clear coated.
In order to play an EM machine you need it to become a part of your body- period. Its almost like driving a real fast but small go cart on a real track, you need to lean, nudge, bump, adjust, CONSTANLY watch the ball and make adjustments to how your working the flippers and the machine as the ball begins to come back. The single biggest thing my friends and I have found, maybe the two biggest things...
1- THEY ARE HARD GAMES. Seriously, seriously hard- the ball will drain more often than not through the side outlanes if you do not know how to nudge.
2- Nudging is a seriously fun thing, it requires timing, feel, and a lot of practice.
We still have yet to hit a 100,000 point game on 5 ball!!!! But, our games now play a LOT longer and were nearly over the hump in learning how to time the flippers and aim at the same time to get a good hard shot.
In my opinion, much of the complaint about them being slow, underpowered, boring etc etc is because some of the EM games are slow, boring, and no fun. BUT. if you pick up one that has a diversity of playfield targets, a reasonable rule set, its a challenge unlike anything with a super deep box a huge electronic screen and fancy speakers and programmed LEDs with the ball flying all over the place.
They are in my opinion a very different game-
I KNOW that nudging skills and ball passing etc are a VERY big part of modern pinball- but its simply different. The old school sound, lights, bells chimes, feel, weight, and feel are very very different. I find that with my 36 year old original Gottlieb flipper coils and a rebuilt mechanism that yes, the game is weak- difficult to get the ball up the play field, hard, and generally boring.... until you figure out that its all on you. If you get your flipper timing down, nudge at the right moments and generally learn a different style of play... suddenly the ball is slamming to the top of the play field, even moving so fast that you have to be damn quick on the flippers to catch it- not for the whole game... but man when your "ON" and playing well.... its a whole body experience- very very rewarding.
To me, if I was looking for another (and I am, but I know the machine I want and only 600 were made).... I would look for theme and colors that interest you, then find a game with a decent number of DIFFERENT things to shoot at. MANY of the EM's of the late EM era are basically just a crap load of drop targets- cool if your into target shooting but I favor a more open style of play so I found one with a vari target, a roto target, and a few bonus targets with the usual pop bumpers and roll overs and I love it.