This looks AWESOME! I'm guessing that the redesigned affected zones will be available to everyone regardless of purchasing the expansion, and its only flying mounts and the lvl 85 cap and archaeology and the new races and class combos that will require the actual purchase. The Barrens was one of my favorite early areas to run around in, so I'm completely intrigued to see what becomes of it.
You believe me, don't you? Please believe what I just said...
From friends I have at Blizzcon asking around, it sounds like it may be a continuation of phasing for parts of it as well - they're streamlining old zones and changing around levels for areas (as an example, Azshara is now going to be your level 10-20 goblin leveling zone) but there will also be further changes occuring due to your doing quest lines as well.
It's easier to play than I thought it would be, but I can't pull off a finisher outside of the tutorial. That kind of ruins the fun for me. The "tag team" aspect doesn't really fly when all the characters feel the same to play.