Ok, I finally got Vista because I went to a store and they really convinced me. They spent 30 minutes going on the web and checking out all the problems I've been worried about.
I'm shocked they didn't try to sell you something they no longer sell -- XP.
There are endless XP vs. Vista threads and reviews and blog entries. A lot of people prefer XP, because it is more "mature" -- meaning it has been around longer so MS has had more time to find and fix its problems, compared to Vista. And, the activation/privacy "features" in Vista really irk a lot of people.
SP1 for Vista is coming in the 2H of 2007. That will help to catch it up to XP in maturity, and by SP2 (late 2008?) it will probably pass XP, in terms of maturity.
Vista will run your XP games just fine, even if you have to use the compatibility mode here and there.
So, load up the Vista you bought and have fun. For most users, it really doesn't make a huge difference whether you use XP or Vista.