A few random thoughts from what I've seen so far:
Warhammer is not World of Warcraft
There are UI similarities, etc etc, but the two games are not identical. This would seem to be an obvious point, but a fair chunk of the WoW community seems to think otherwise. Honestly, that's part of why Blizzard's Wrath hype on Warhammer's launch week may be misguided; most Warhammer players will be glad to fill pages of commentary about what's wrong with WoW, while fans of WoW's PVE probably won't find enough depth in Warhammer's PVE game.
Anyway, case in point, I rolled up a White Lion, Warhammer's melee pet class, during the open beta thinking that I might like it because I liked the melee pet aspects of Death Knights. I wasn't that impressed. I also thought that I would NOT like the game's two "turret" classes (the engineer with actual gun turrets, and the Magus with stationary demon pets) because I can't stand WoW's Shaman precisely because of the need to manage stationary totems. Well, the whole mechanic is upended in Warhammer because your action points (mana/energy equivalent) regenerate rapidly, even in combat. So, where totems make your Shaman go OOM faster and have to sit and drink (forcing you to decide whether the benefit of the totem is enough to help you kill faster to offset the mana cost), the Engineer isn't looking at a huge loss for redeploying his turrets.
Did Mythic deploy enough servers?
WoW's original launch was a clear case of not enough servers. Far too few were available on launch day, and the addition of new ones even later the same day came too late. Crowded MMORPG servers tend to get MORE overcrowded as new players go to join their friends or at least go to servers with a larger economy and more guilds. By contrast, I was very very concerned about the small number of servers at LOTRO's launch a year and a half ago... but it turned out that the ones they rolled out for open beta were sufficient to hold everyone who showed up.
As of 7 PM (EST) tonight, Mythic had rolled out 49 servers. Seven of those servers had queues on the Destruction side, while a smaller number (maybe 3ish?) had queues on the Order side. I have no idea which of those servers have been around since the Collector's Edition headstart happened on Sunday, or how many opened today. (This is relevant because the queue is lower on servers when they first open to accommodate the rush on the newbie zones; i.e. I don't know whether the queues are on brand new servers or not.) Also, not everyone may have decided to bother with the download for the Head Start (though, in LOTRO's case, it seemed most everyone did). Then again, folks on the West Coast aren't even home from work yet.
On the flip side, Keen complains that his server seems UNDER-populated. I'm guessing this is why Mythic was initially cautious with how many servers to roll out. We'll see if they got the numbers right.
Yep, still NOT World of Warcraft
JoBildo explains better than I can how Warhammer isn't as much fun if you're not in a group. Sure enough, I noticed that today with my newbie Dwarf, as there weren't enough people to really attempt the second PQ in the Dwarven starting area, and (despite an overwhelming Greenskin presence that completely wiped out the zone control meter) my scenario queue didn't pop in nearly an hour. My initial instinct was to go for the least populous realm possible to avoid queues. I took Mythic's "please go play Order on Sea of Malice so our pop balance doesn't go to crap" invitation, but I may need to revise that stance to go somewhere with more people I know to help the guild acquisition process.
Bottom line is that I had a good time on my second first impression of Warhammer (though selecting myself while attempting to loot corpses is still freaking annoying). I don't know how long I'll be playing this game, but it's certainly looking like it'll keep me entertained for a few months.