Classes have changed. Your warlock may not be as much fun and your paladin is probably not as boring. Your main may no longer be the class you have the most fun playing. Of course, I'm an altaholic, so I'm enabling here, but I do think that you shouldn't spend time struggling on a class that isn't as much fun as another one that has been newly tweaked to be more for your playstyle.
Inscription is new and the rest have been improved, particularly the gathering professions. If you stay with what you already have, go see your trainer to get up to date. Oh, and beware of sticker wow gold shock. If your professions were maxed in Burning Crusade, you can update them all in the starting cities in Northrend, but it costs hundreds of gold. Don't sweat it if you don't have enough to do it right away, gold is easy to get these days and you'll be caught up in no time.
In order for casual players to get the most out of their playtime, it really is best to schedule out blocks of playtime that allow you to balance the rest of your life and coordinate with your family. You will find yourself having wow gold longer, uninterrupted sessions if your scheduled playtime is considerate to (and approved by) your significant other, children or parents for those who are still living at home.