If you analyse Sid Meier's games you'll notice that complexity entered the company in form of Brian Reynolds and other developers. I'll start from Beginning:
Pirates! - average complexity game; developer - Sid Meier
Railroad tycoon - average complexity game; lead dev. - Sid Meier
Railroad tycoon 2 - more complex than RRT; lead dev. - PopTop
Civilization - average complexity game; lead dev. - Sid Meier
Civilizaition 2 - more complex than CIV1; lead devs. - Brian Reynolds, Jeff Briggs
Colonization - more complex than CIV1; dev. - Brian Reynolds
Alpha Centauri - most complex Firaxis game (at least in theory); dev. - Brian Reynolds
Civilization III - a bit less complex than SMAC; developers Jeff Briggs, Soren Johnson
Civilization IV - as complex as SMAC; lead dev. - Soren Johnson
C4: Colonization - basically a copy of original
Pirates! - basically a copy of original
Civilization: Revolution - average complexity game; lead dev. Sid Meier
Civilization V - average complexity game; lead dev. Shafer
Sid Meier, personally, always put entertainment over complexity. Even repeatativeness over complexity.
Sid didn't like where Reynolds was going with his designs so Reynolds quit. I don't know what happened with Briggs and Johnson but I guess the issue was the same. Why fire or bid farewell to someone who does exactly what you want?
We have a saying in Croatia, uhh translation goes something like "Why switch out a horse that's already winning the race?" Sid Meier obviously thinks
gameyness and
goofiness did more for his career than complexity and longevity.
I have my opinion on that and its not pretty. But surprisingly I like CIV5 very much. So sue me