First, I must say that the carousel is constantly changing from one Android version to another between horizontal and vertical layout, as though Google's developers are uncertain themselves which variant is appropriate. The carousel is used intensively, so even a little flaw in its design brings big problems. I'm currently speaking about standard Android in general, and standard Android 5 in particular. Other customized firmware may be free of the issues I'm going to describe.
In Android 5, the carousel is always vertical on my pad. Well, it could be appropriate for portrait screen orientation, but the carousel remains vertical even in landscape mode. When you try to flip through the apps from bottom to top, you will constantly activate the central button of the navigation bar, floating in foreground (over the carousel!), especially because the button has an enlarged sweetspot, because it's Google button (it invokes "Google App" including quicksearchbox and other stuff). It took me a long time to get accustomed to the new - not so convenient - practice: in order to swipe apps from bottom to top, one should swipe from center! Otherwise you'll get into the Google app.
That's how it was since Android 5.0. In Android 5.1 they introduce new strange bug in the carousel. It does not work when you tap an app in it first time. After the first tap the carousel is closed and the launcher is shown. Only if you open the carousel second time, it works as expected.
I know, this is far from the main subject of the blog, but at last it's all about Android. And I'd prefer that Android would not prevent me from working with my applications.