I spent the past few days on reading the "Races and Classes" as well as the "World and Monsters" preview books of the 4th edition of Dungeons & Dragons. After that my personal opinion about the 4th edition is that it is going to be really, really great! :D
While reading these two books I noticed that every thing I didn't like about the 3rd edition will be revised. By some points I even did not know that I did not like them! But for those who are afraid that always the good parts of 3E will be changed, it should be a relief to hear that it seems for me that all these parts will be left as they are.
One of the biggest changes is the new cosmology which I like much more. (I'm already planning my first campaign based on the new cosmology.) In the 3rd edition I disliked that there was the enforcement to have a plane for every element, alignment and so on. That was much to complicated and most planes were just useless (how should you travel a plane consisting only of fire?). The new cosmology has only the planes which are really needed and are really cool!
As you can see I'm really excited about the fourth edition! It's hard for me to wait the 30 days left to the release.