Well I'd love to give you first impressions of the Burning Crusade, but the only land I've visited is Outlagg. So far, my realm, Thunderhorn, has been all over the place tonight.
I started out by taking my Shaman to Outland-- Hellfire Peninsula was up, but lagging so much I couldn't even get off my mount. So I pushed inland, to Shattrath City, where I got my first quest done (the tour of the city is fun and easy, and gives you a little lore, a little XP, and that nice Aldor vs. Scryer decision). Eventually, however, that too was lagged. My friend and I then decided to start up our Blood Elf alts (I'm doing a mage), but while there were plenty of player Blood Elves in the starting area, the NPCs had decided to stay home. It's about then that the world server crashed, kicking us all off.
Later I tried to run Hellfire Ramparts, and we started rolling, even as the Outland server crashed (all of our guildies exited the game). Unfortunately, we had a bad pull, and wiped, and then as soon as I released, the server did a "what the??" (because it wasn't there), and kicked me out of the game again. Our instance group is going to try again later.
It's too bad, because everything else I've seen of the expansion is terrific-- the lands look great, the story is deep, the music is terrific, and the items are droolworthy (even the few greens that dropped in the instance made us all go "whoah", and we're in Tier 2 sets). If it weren't for the lag, things would be great (and on the less popular servers, things probably are). But considering how many more people are going to be picking up BC and playing this weekend, outlook not good for Outland on the high traffic servers.