Honestly the more I read about the next expansion, the less I want to play warcraft during the expansion. First off, everyone and their mother will be trying to play a death knight, and while they're going to be incorporated in raiding, there will be so many people trying to play it, that a majority of people won't be able to actually get into raids.
Slow down there, Negative Nancy. There wasn't exactly a huge influx of raiding paladins and shamans in TBC; if anything, there are far fewer of them than other classes.
I imagine for pvp they'll be initially overpowered, then the people playing other classes will QQ so much that the DKs will get severely nerfed in pvp, to the point where they will have more flaws than bonuses.
What on earth are you basing this assumption on? Blizzard said that they will be no more powerful than the other classes.
And leveling... leveling 1-60 was a pain, 1-70 made me want to stab myself... I cannot imagine trying to do 1-80.
Blizz said that there will be some mechanism to make 1-68 easier.
But hey, if you want to play WAR, I'm not stopping you.