WordPress is the kind of software that nobody likes to hack on. Specialy when you don't have to create a simple blog.
"What? Not a blog? Forget about WordPress and use another tool/framework." - That's what I thought, but actually I took less time to use and extend it than I've expected.
The first feeling I've had when started working with it was like: "oh god, what a crap, global functions everywhere, I'll take months to write all the features.".
I've ended up customizing the whole way WordPress works at the frontend, and at the end I realized that it really helped to speed-up my development time.
Here is a list of resources that was really helpful to me: https://github.com/endel/awesome-wordpress/