By default, the entire iTunes window displays your content in what was previously called Grid View. The sidebar is hidden, though you can display it by pressing Command-Option-S or by choosing View > Show Sidebar. List View, which you can access it by clicking List in the header bar, is still available for content other than Music; but Cover Flow and Album List views are gone. In the Music library, this is called Songs view.
Classical music fans are out of luck with iTunes 11. The only way to view your music by Composer is to use the hard-to-navigate Songs view. Neither the Artists nor the Genres view provides a Composers column; and the Column Browser, which could simplify matters, is available only in Songs view.
You can view playlists in a new way. Click Playlists in the header (the sidebar must be hidden for this option to be available), and you'll see a sidebar that displays only playlists. A pop-up menu above the list offers access to your different libraries -- Music, Movies, TV Shows, and so on. Another pop-up menu, this one at the right side of the iTunes window, provides access to your iOS devices.
With the new Playlists view also comes a new way of creating playlists. Click the Add To button at the right of the iTunes window to show a two- or three-pane display. On the left are Songs or Albums in a single pane, or Artists and Genres with a list to the left and content in the middle. Your playlist is on the right; you can drag items to it, and click Done when you've finished.
Curiously, if you have the sidebar displayed, you don't see the Add To button when you click a playlist, and you have to manually drag items to the playlist. This surprising situation is one of the many inconsistencies in iTunes 11, where controls appear and disappear according to what you are viewing and how.
All of these view options are essentially the same for other types of content. I've focused on music here, but movies, TV shows, books, and so on, inherit the same options.
If you're accustomed to using the iTunes DJ playlist, you'll have to adjust to its quite different replacement, the new Up Next feature. Whereas iTunes DJ could extract tracks from a selected playlist or from your entire library, Up Next plays only what you tell it to. You can select items, right-click them, and then choose either Play Next, to play them after the current track, or Add To Up Next, to add them to the upper part of the queue, in front of what was already there.