I wrote on many frameworks so I wanted to write something on cms. I took WorPress because its the most popular blog cms I know and started learning it. At First I dislike but than I really like it. In few words its sounds like "You have instruments like posts, taxonomies, users, comments, settings and something else, and You can manipulate it like you want in Frontend". Also WordPress have many free plugins but they wrote not so good or with banners, so you need make some correction. We I like wp its because its very popular so You can find a lot of information in google also You can found plugin that you want or similar for you requirements so you don't have to write plugin from the begging. Also I spent three days looking inside wp code and I can say that this project not object orientation there are a few classes and a lots of functions. At the end of my traveling to the code I understood that It's cool because people who don't know programming, like work with function then with classes. So that is why WordPress have so many themes and plugins.
P.S. When I am writing my blog I manipulated wp instruments like I want. I had no limits so its cool and I didn't need to write some code in wp.
Also You can download github.com my portfolio plugin that I built from another two wp plugins.