If I could be directed to a topic explaining the changes or someone give me a short summary, that would be great. Basically, what did I miss in 2 years?
I don't think anyone threw together a topic that documents all the changes. Miromiro's guide will bring you up on stuff that you probably hadn't noticed (ie, You could follow topics before the update) - http://gtaforums.com...k-newbie-guide/. It hasn't been updated since the update though, so there's nothing about the new interface. AceKingston also tried to put together an FAQ, but there's not very much there (In his words "it's mainly just an faq guide") - http://gtaforums.com...the-new-layout/.
Kinda like with the old forum you just have to get a knack for things by using them. Everything you can do is in your settings still - http://gtaforums.com...e&module=usercp which is mostly the same as the old control panel except that flags and custom skins are missing, and you can now ignore people and change your displayed name once a year.
Most new changes are posted in the GTA Network support section which combined the announcements and old network support sections. http://gtaforums.com...etwork-support/. If you have any questions or issues you should post them in there.