You might want to check out this post for info on how to restore the (far superior) 2.0 spellgems.WTF do these spell gems mean!!!
For the love of god, the my UI is broken!!!
If you're dead set on clinging to your old custom UI, see this post for instructions on how to update it. It's also possible that you'll start seeing some necklace icons here and there where some new item icons have been put to use. If this is the case, you'll also need to pay a visit to this thread for info on how to fix that problem.
Since you're coming back from a long break, I'd recommend you just find a new, more modern UI. Either that or borrow one from a friend/guildmate.
Welcome back!