WordPress is a great system for personal semantic publishing and is more than adequate for the vast the majority of websites. No other CMS can match it for simplicity, ease of use, breadth of plugins, and an active developer community.
However due to its blogging background it has one very substantial weakness. Namely there is no way of easily relating one post to another and detailing its realationship. Of course taxonomies can be used to group posts and provide some form of relationship. However this is not an elegant solution.