So far, so good. I tried out a few of my characters, and here are some suggestions to help you get your characters up to speed.
1) Get your glyphs. Review all of the glyphs for your class and see which ones you want to use based on your spec.
2) Visit the class trainer. No matter what level you are, you probably have at least 1 new skill to learn.
3) Review all your spells and abilities. A lot of spells and abilities have had some type of change done to them. Your are playing a whole new class essentially.
4) Respec. All of your talents have been zeroized and all the trees are brand new.
5) Be patient. If your performance is not at the level it was before the patch, Blizzard will see this and make adjustments. You can also post on the offical forums and describe what you are seeing. Make sure you include as much detail as possible. What you were doing, what abilities you used, etc. Just saying you are doing less damage, for example, will not be very helpful.
6) Have fun. Everything is changing. Take some time and learn the game anew.