Although Apple never mentions it except through the hint in the name, El Capitan is clearly the Snow Leopard release of modern OS X. We'll never know if it was really Apple "listening" to the rising complaints of its most loyal users, or if this was part of the plan all along – but we seem to have gotten what we wanted either way.
Rather than rushing forward into crazy new complicated features, Apple has taken a year to solidify its foundation. El Capitan is not a lackadaisical update. It is packed with small niceties and big performance upgrades which are going to improve the experience of using OS X every day. Metal offers to usher in a new era of power in professional apps and games, and App Transport Security will keep our data safer in an age where it has never been more at risk.
Feature-wise, OS X 10.11 El Capitan represents a change of pace that is both much needed and much appreciated. Reinforcing the old before continuing to build out with the new. We don't need insane new features every year nearly as much as we need stability in the system overall. I'd love to see OS X (or perhaps, macOS?) 10.12 come out next year with some mind blowing new features for me to drool over, but only if they don't compromise any other part of my system in return.
For this year at least, El Capitan represents a stable and well thought out release. It is a solid update, with features that everyone can use and enjoy, and no noteworthy trade-offs.
Who could complain about that?