(Looking some facts up, Knizia wrote an article describing a game in 1985. Really, he didn't have a game published as, you know, a boxed item until Digging and Goldrausch in 1990. If you really want to get persnickety, he didn't knock one out of the park until 1992 with Modern Art as far as starting the Era of Kniza. Still, I count 1990 as the start, which is still a good twenty-five years.
(Mind you, Wolfgang Kramer published his first game, Tempo, in 1974, which uses the same system as Top Race or Daytona 500. Man, but Kramer is in it for the long haul)
When I first started really playing board games, Knizia was one of the rock stars of the hobby. He was one of the big names and he was my favorite designer for a while. I've bought and played a lot of his games over the years.
These days, his star has fallen a fair bit in the hobby. His output has declined. He has been focusing on the family audience and the iOS market. And, he's kind of an anti-social (or shy) guy who definitely treats game design like a business.
In a world where there's a growing market for the hobby gamers specifically and where Kickstarter has been adding more and more of a personal, social touch to game designers, Knizia seems 'out of touch' with the dedicated hobby gamers.
Mind you, I don't think that's hurt the man at all. To the best of my knowledge, his games are still selling like hotcakes and many of his titles have been in print for years, even decades. He may no longer be the cutting edge for hobby gamers but he definitely knows the broader market.
For me, he was at his best from 1992 with Modern Art to 2006 with Blue Moon City. Some folks might use Tigris and Euphrates as the start in 1997 and might go as late as 2008 with Keltis. No matter what, that's a decent span of time to be putting out a lot of great games.
Speaking as a former member of the Cult of Knizia and someone who is still a fan of many of his games (just so you know I'm really biased), I think that Knizia was a key component to the modern board game environment and some of his games are still going to be played twenty years from now.
That's because many of his best designs are simple enough that they can be explained in ten minutes but still offer a lot of complex choices and serious interaction. In other words, they are awesome family games.
OK, maybe I am still a member of the cult. You know, part of the reformed sect as opposed to orthodox one.
I don't know what Knizia's future will be but his last will be a part of the hobby's future.