DK's are a fun toon to play, VERY TOUGH TANKS with the plate gear, and the quests actually give you nice blue gear rewards that are far better than what you could buy in the auction house etc.
My choice for my DK was a female Night Elf... she kicks serious *censored* and can shadowmeld if the mob is too much for her as part of her racial inherritance of being a night elf.
Also the AOE ( Area of Effect ) casts that do not require Mana! Is awesome, you can both be in the mob pit hacking and slashing axeing them down and cast DOT ( Damage over Time) AOE's to bring death to all enemies around you.
Still havent found the weakness to the DK, but to have a balance in the game there has to be some weakness, whether its FEAR SPAMMING from a Warlock or whatever it may be that affects all others anyways.
I have played for 2.5 years and the social aspect of the game is what really keeps it going for me. Dailys just get plain boring, but the interaction with other people is priceless at times. Met lots of good people and continue to do so. So its a gamers chat room for me at times. Also it helps to not just have 80s, but also have some new toons to run dungeons etc with the chance that you could die etc vs becoming so strong and tanked out with the best epic armor and socketed gems for theri stats that you become godlike and it gets boring if you dont have to worry about dying in the game and swat bosses like flies. Without a challenge it gets old fast if you are playing the game, just to play the game not not be social.