I made a mod that lets you beat Portal 2 backwards, starting from the final boss, ending with the relaxation vault.
This is possibly the most satisfying experience I've ever made in Portal 2. Tailored to both casual players and speedrunners.
Reverse mod is now available as part of Krzyhau's Portal 2 Speedrun Mod and is receiving regular updates! To download it and play it for yourself, follow the instructions on this page: sm.portal2.sr