In RHEL, you might encounter this error, when trying to run the unity editor after (apparently) all dependencies are met.
Unhandled Exception: System.TypeLoadException: Failure has occurred while loading a type. at MonoDevelop.Startup.MonoDevelopMain.Main (System.String[] args) <0x40c2ce80 + 0x0000f> in <filename unknown>:0 [ERROR] FATAL UNHANDLED EXCEPTION: System.TypeLoadException: Failure has occurred while loading a type. at MonoDevelop.Startup.MonoDevelopMain.Main (System.String[] args) <0x40c2ce80 + 0x0000f> in <filename unknown>:0
You might still be missing gtk2-sharp (required by Unity Editor), and gnome-sharp (requirement by the mono develop ide).