I've barely played CK2 and haven't bought any Paradox DLCs since the Rajas of India DLC I eagerly bought with great anticipation rendered the game unable to play on my and many other computers, in addition to containing many problems that should have been spotted almost instantly by any playtesters and others which were not instantly obvious but I felt should and would have been found with any adequate testing. That was three DLCs in a row I consider to have been released in a state that made me feel like an idiot for buying them at release instead of waiting a few months for patches and 75% off sales, and three was my limit (particularly as I've seen nothing from Paradox that indicates they feel there was even a problem, or that they plan to do anything to prevent it happening in future).
Don't want to touch on a lot of the stuff in this thread, but we really haven't been happy with the quality of some DLCs. I was unhappy to the point of doing 100+ hours of QA on RoI in my spare time both before and after release. But finding bugs doesn't equal having time to fix them, and not all bugs are even present for the entire testing period. On the plus side, team CK2 has an additional programmer now, and I plan to test Charlie myself earlier in the process.
I also linked MeinTeam's post #101 about unclear UI stuff, sent the link to our UX guy although he is aware of many of them already.