Quoted from emo:+1 here. I find the game-play on many of them excellent. They have been steadily improving over the years.
I don't think so, they have been getting worse. The height of Stern was 2003-2004, with the depth in LOTR TSPP and RBION. SM was an exception, but all in all they went down fast. I haven't spent much time with tron to really know if there is any depth in it, but the TF PF just doesn't do it for me.
There are quite a few WPCs that were not that great, but far more Sterns that failed. These are also different times as well, so it's hard to say. There were some very williams'ish DE machines in the early 90s.
I think people confuse the feel of Sterns. Many associate different than b/w to be cheap, when it is just that, different.
Stern staying alive is massively important, and they make some great games. Even in the early days they never had the staff or capital that b/w did, so it's hard to ever compare them to the great b/w. They have continued making machines in the way they have for a long time now.
We all have benefited from them holding the flame, regardless of the era or type of machine you like.