Version 2.2 is an update on GIMP 2.0. GIMP 2.2 is fully backward compatible to GIMP 2.0. Plug-ins and scripts written for GIMP 2.0 will continue to work and don't need to be changed nor recompiled to be used with GIMP 2.2. We do however hope that plug-in authors will update their plug-ins for GIMP 2.2 and adapt the GUI changes we did with this version.
GIMP 2.2 replaces GIMP 2.0. It is advised that you uninstall GIMP 2.0 before installing GIMP 2.2. If you want to keep GIMP 2.0 installed in parallel to GIMP 2.2, you have to choose a separate prefix which is not in your default library search path.