I've played a lot of Gottlieb pins, and I rather like them - there were some great games. Arena and TX-Sector come to mind. Not a huge fan of Genesis, but it's still good. Overall, I have liked several Gottliebs... and not liked several. I think they've developed the reputation of just being "meh". Add to that the fact that it's a royal pain in the neck to find manuals for them, and they become annoying to work on.
That, and every Gottlieb I've ever worked on has needed those stupid ground plugs cut off and crimped into eyelet connectors, then screwed to the transformer housing. That fixes a lot of stuff, actually.
Another thing I've noticed is that a lot of Gottlieb translites fade badly, and the art in general isn't as nice as a lot of the Williams games. Similarly, they had several "wannabe" themed games - like Raven. It wants to be Rambo, but it didn't want to pony up the cash to license Rambo. Also, the score displays they used are those tiny VFD's. Some games like TX-Sector even had them all the way at the top of the headbox. Kind of annoying when you want to glance up at your score while playing. The displays do seem to last forever though.
So, it's probably just a lot of little things that strike against them. They're not bad pins at all.
-Ian