Lots of folks have tried to force Wordpress to be more than a blog platform. I've always seen these efforts in the same light as when guys dumps tons of money and time squeezing horsepower of a Honda Civic: end of the day, it's still a Civic that get its lunch eaten by a stock 'Vette.
Look, you just don't get power and flexibility in the same package as intuitive and simple. The best you can do is cut one to boost another. Take iOS. Intuitive as hell. Flexible as a piece of rebar.
Drupal's been mentioned in other comments. It's crazy powerful and very flexible... it's the Corvette to the hopped up Civic that is Wordpress. It's also hard to learn, the interface can be...challenging and the plumbing is complex.
Edit: Downvote me if you must but at least communicate why...did you build a 11 second Civic or something? ;)