To that point, you can generally also force quit an open app by clicking and holding on the dock icon for the app. If the system knows the app has tanked ("not responding"), Force Quit will automatically be in the menu. If the system doesn't think the app tanked, you can press option and the Quit option will change to Force Quit.
Occasionally, though, Cmd-Opt-Esc is useful merely because whatever app that is tanking is slowing the UI way down and you are not able to change app focuses or access the Dock. In that case C-O-E can usually still get you a list of open apps so you can kill something. 🙂