Quoted from kguenther6:
Single players can keep features between balls so tend to have a little more to them. Multiplayer EM's can't do that. There are a lot of great single players that are fun and not a lot of money.
Here's Clay's take from pinrepair.com:
Why Single Player Games?
The reason single player games are more desirable than multi-player games is simple: game play. Single player games have deeper rulesets, and award more Replays for acheiving game goals. Multi-players games *must* have less rules because there is no memory in these EM games. That is, the game can't remember how far along in the ruleset a player has gotten from ball to ball. Hence multi-player games have a goal that must be achieved in a single ball (the rules are less sophisticated.) And multi-player games usually only award Replays based on score (not on game goals), so there aren't multiple strategies to winning replays (until the 1970s). Finally multi-player games are bigger, uglier, heavier, and more time consuming and difficult to work on.
Are there any "good" Multi-player games?
Yes there are, mostly in the 1970s. Starting about 1971, Gottlieb made heavy use of the modern style drop target and 3" flippers on their pinballs. So many of their single and multi-player games during the 1970s have drop targets. This gives the player a lot to shoot for, and makes those games pretty darn fun. Though I still prefer single player 1970s gottlieb pinballs to multi-players, a lot of the multi-player games have great game-play too. The best thing about 1970s Gottlieb multi-player games is the "bang for the buck". That is, they are inexpensive to buy, yet provide a lot of fun to play. The downside is they are bigger and more complicated to repair than single player wedgeheads, and the rulesets are shallower.
What About 1970s Drop Target, 3" Flipper, Gottlieb Pinballs?
Aww a soft-spot in my heart! The Gottlieb EM pinballs from 1971 to 1979 with drop targets and 3" flippers are amoung some of their best games (especially the single player versions). Frankly they didn't make a lot of titles during this era (just 8 years worth), compared to 1947 to 1970 where they made lots of 2" flipper games. With that in mind, 70% of all Gottlieb production was of 2" flipper games (compared to the 1971-1979 three inch flipper titles). Luckily production numbers are higher during the 1970s, but the number of titles with drop targets and 3" flippers are limited. And these games are quite fun. The 1970s evolved the EM technology to its limit, with advanced features and ideas.