Is the ILS CAT III system the most complex landing system available?
Yes ILS equipment for CATIII is the most sophisticated across ILS systems. As people mentioned in comments there are another types of landing systems, which could be more complex.
No it is not auto landing system.

It self CATIII is a category of a landing conditions.

Also take a look here What is different between a Cat IIIA, Cat IIIB, and Cat IIIC ILS approach?