You must train to the logic of the questions, they are tricky, multiple negative/exclusive.
There's little to do on the content if you're experienced enough on all domains.
The difficulty of questions in the exam vs what you may find on the web or apps is important.
Don't understimate having a good knowledge of the CBK, because you will spend solid minutes figuring out what is the point this short one-sentence question, and how it relates to the topic you thought to be an expert on.
Yes I think that you will still need to have a systematic study on all domains, and practice on various exam prep questions. CISSP exam is far more thorough and detailed than some tutorial videos and a few sets of downloaded questions. If you don't, chances are that you will be wasting your time and money on the exam.
Check out Amazon and read the reviews on various books. ISC2's CBK is good but not enough. Personally I would not recommend Shon Harris' book, too verbose and often off topic. Anyway, besides ISC2 CBK, pick two other books and do a focused study, especially on the domains that you are not familiar with from your work experiences.