Reminders.app on OS X is somewhat limited and inconsistent, but for its simplicity offers a lot of possibilities. For many this is all they need to keep control of their tasks and reminders.
Sven Fechner has a nice list of tips, tricks, and links for the OS X Reminders app. I use Reminders every day through Fantastical 2 on my iPhone, but I have to rely on Apple's apps on my iPad and MacBook Air. I would love to see better consistency between all platforms (just one example: clickable URLs in notes).