Still in the spirit of doing in the beta what I won't do in the release version of Wrath of the Lich King, I copied my level 70 Warrior there. The good news was that in spite of him having only average level 70 blue armor, I could tank the first dungeon, Utgarde Keep, just fine with a 61-point protection talent build. The bad news was that even with some searching I found nothing in the current version of the WotLK beta which would significantly cure the problems that Warriors have in TBC.
First of all, if Blizzard plans to allow people to have two talent builds and switch easily and cost free between them, that feature isn't implemented in the current beta yet. Well, in the beta any respect costs only 1 copper piece, but that is just for testing, and won't make it into the release version. Thus the biggest Warrior problem, that they can either tank or deal damage, but not both, isn't solved yet.
Then I looked through the various new Warrior spells and talents, and found very little which really changes the way how a Warrior is played. For example the 51-point protection talent Shockwave isn't really all that great in practice. It suffers from the same problems as Thunderclap, that it'll break sheep and other forms of crowd control. And the 3-second stun. At best it combines abilities of already existing Warrior abilities into something which might be useful for AoE trash tanking. The 51-point Fury talent Heroic Leap is just a fancy-looking Charge. Many of the other new talents give you X percent more of this or that, but don't add any new game mechanics to the Warrior class. The new spells are just the same, there are even more rank upgrades and fewer totally new spells than in TBC. I've already heard mages complaining about the same, not sure for which classes the same is true as well. I know the paladin class is being much changed. But a Warrior at level 80 will play pretty much the same as he is playing currently at level 70. WotLK does not reinvent the Warrior class.
I tried an arms/fury spec for maximum dps, dual-wielding two-handed weapons with Titan's Grip. Even with 5 talent points put into that ability, you still suffer from a 20% speed penalty, which turns Titan's Grip into a talent which doesn't give more added damage than any other talent. Yes, with an arms/fury build you deal decent damage, but unlike a Death Knight you don't have any talents to heal yourself, and thus suffer from longer downtime between fights. Some people claim that MS Warriors dominate PvP, but that isn't true. They dominate PvP only as much as rock dominates a game of rock-paper-scissors, seen from the view of the scissors. They are flavor of the month sometimes in some arenas, but there are no data in the armory that suggest that Warriors would be generally better than other classes in PvP.
There will still be endless arguments in the coming months whether Death Knights are better or worse than Warriors in PvP or tanking. But there is no doubt whatsoever that Death Knights are better for solo PvE. They are what used to be called a "tank mage", a class without weaknesses, having both good offensive and defensive abilities. Death Knights even have self-heals, for gods sake! They are a complete tank, healer, damage dealer trinity rolled into one. And they can do it all with one balanced talent build. In fact due to how runes work (see post before), a balanced talent build might work better for them than a specialized one, unlike other classes.
That doesn't make Warriors obsolete. They still will keep their role as preferred main tanks for most raid bosses, and probably for heroic dungeons as well. But unless Blizzard really implements the talent-switching feature, which they occasionally think about, but haven't really even promised yet, leveling a Warrior is just a hard task you do in view of a main tank career later. Anyone who ever tries a Death Knight, and I guess most people will do, will have a hard time going back to playing a Warrior. I don't know exactly who will do more damage given equal equipment, but the Death Knight has so much more utility and abilities that just make his live easier. Death Knight is the ultimate soloing class, while Warriors even with the new talents and abilities still rank among the worst classes to solo with. My Warrior is now retiring and spending his old age as a pure alchemist, until Blizzard makes Warriors as easy to level as Death Knights, which they probably never will.