What's the difference between regular WordPress categories and review type taxonomies?

Let's say I have two review types: Movies and Music. Let's say my primary taxonomy for Movies is Genre and for Music it's Artist. Now, lets say I usually write 3 different types of posts generally speaking: Newly Released, Classics, and Announcements. So, in my Movies mini-site I will have reviews about newly released movies, classic movies, and announcements about upcoming movies (announcements would not be reviews and would have the rating information hidden so they look like regular posts - see theme documentation or the FAQ for information on how to do this), and I will also have those same three general types of posts in my Music review type. So, I create three standard categories: Newly Released, Classics, and Announcements. Notice how all three of those categories could be applied to any types of posts, both reviews and regular. Then I put those in the menu so that when I click on, say, Classics, I am taken to a post listing page of all posts or reviews in the Classics category (I will see both Music reviews and Movie reviews listed together). However, if I click on one of the artists within the Music review type it will keep me within the Music review type and only list music reviews, since that has nothing to do with my other review type(s).

This is just one example. There is no one right way to setup your site. You can do it a million different ways, whichever best suits your site and how you want to organize your content.