There are several rules which have been revamped. The two most notable ones are a completely different assault process and a new method of attaching independent units to formations which is dependent on a rating on each of the leaders. This numerical rating doesn't exist on leaders in TDC.
I am in the process of compiling a document with changes between 1.1 and 2.0. Before I make it public on BGG I need to verify it and also proof read it for spelling errors (since I am not a native English speaker).
If somebody is interested in helping me out, just drop me a mail and I can send you the pdf.
Disclaimer, this might not be complete or accurate, since this is only to help me more easily move between the different titles in GTS.