Some of the things I did not like about WoW gets solved with my new Death Knight character. I don't mind leveling up a character once. I enjoy doing quests and following the storyline of most MMORPGs, but then if I don't like my character at the end, I won't play through all the content again with an alt.
I don't like my WoW priest. I don't like her in PvP and I never enjoyed being a duckfooted troll.
WotLK solves this for me by starting me out at level 55 with a Death Knight. First Death Knight is a super fun kick ass class to play. Second the new starting area which got me up to level 58 was really fun. I wished there was more.
Third once out in the world, I have just been having fun with it. It can blast through MOBs unlike my priest who must single pull everything. It can actually win a fight in world PvP where my priest always lost because I play casually and am not willing to do the item grinding or perfecting of play to make her viable.
Fourth, I don't have to stop constantly to drink water.
Fifth, I only have to get level 70 before I can do all new content in Northrend. After a weekend of play, I am level 62 already.