My personal favorites are those games with simple rules and deep strategic depth and I play them regularly online or with other people who love those games in particular. I am also in two general boardgame groups and they both much prefer the complex rule games, I'll give my best guesses as to why.

1) They like the worlds of the complex games, building societies or facing some major broad challenge. 2) Elaborate games are so open-ended and hard to analyze forward strategically that they are much more balanced across people of different skill levels. People who would have no hope of a competitive, fun game of chess will have a more interesting game of Brass: Birmingham or Eclipse. 3) The games can be played with a lot of players and involve a lot more human-human negotiation and discussion, rather than pure strategy.

I love the simple but incredibly complex games myself, but I understand why they're not everyone's cup of tea.