The big changes to Cyrodiil after the Imperial City Patch were:

Different campaigns now have different rule sets.
Emperor buffs only apply while you are actually emperor.
Changes occurred to the end of campaign rewards.

Biggest Impact of Imperial City Zone:

You get Tel Var Stones for completing the PvE content in Imperial City. When you are killed by an enemy player, they take most of the stones you are carrying. Tel Var Stones are used for purchasing the new best in slot gear/mats.

Regarding Templars:

If you read the forums, it seems like every class is in a terrible spot according to the folks who play it. There were a lot of nerfs that affected all classes, and stamina builds were hit harder than magicka builds in a lot of ways, but I wouldn't say Templars were hit harder than any other class. A lot of build redesigns had to occur after this patch.

For more detailed info -- here is a link to the patch notes (you can use the hyperlinks in the first post to skip to areas that interest you) http://forums.elderscrollsonline.com/en/discussion/comment/2200151/#Comment_2200151