system3 flippers are easy to fix to make more consistent with other brands. this is well documented at http://pinrepair.com/sys3 for those that care.
system3 are built well, but when there is a problem, often they can be a bit tricky to figure out. Mostly because there's just less base knowledge of the system. the production numbers on system3 games is very low compared to say williams/dataeast (where DE is basically a sys11 copy.) so there's less experiences out there to share.
as for the games themselves, i like the alpha numeric system3 games myself. they are very unique. the dot stuff is decent, but the overall stop and go game play (which most seem to have) makes me weep. i don't like it when the game stops, asks me questions, and i have to give an answer. it just bothers me for some reason.
also the style of dot animations and game play is unique to gottlieb and very different than say williams/dataeast. i don't like it as much personally. the usage of flasher bulbs too annoys me for some reason. these are all small details but it detracts from the game play in my eye.
as for rules some system3 are really shallow and others (like cueball wiz/stargate) are pretty deep. but again the issues outlined above come into play and it changes the experience for me personally.