PLEASE KEEP IN MIND THAT THIS IS JUST MY VERY OWN OPINION!
I'm not sure about the upcoming changes from Cataclysm, but here is my advice:
Warrior: In order to have one of those, you have to get used to keep an eye on your health and always have potions at hand. Skilling your first aid skill and cooking, in order to have bandages and food to make your downtime shorter is a must! But then, you'll have a pretty badass mail/plate wearing kickass toon that will be looked for. Keep a shield in your backpack (Tanks - You're welcome!) because the skilltrees are not that important in the lower levels.
Shaman: I thought it would be nifty to stick some pieces of wood into the ground and cast some spells but boy, was I wrong! While leveling my shaman as enforcer, I nearly never used totems at all, except when I did pull 3+ mobs or took on an elite up to 2 levels above me. Healing spells FTW! It's been a bit boring in the beginning and I have to admit that the fun starts at level 40 but shaman still is some really bad buttkicker!
Druid: You have to have patience with the druid. First, you play a hunter without a pet, then, when learn to transform into the bear, you play a warrior until you get to transform into a kitty, playing a rogue from that moment on. I never played a druid up to level 80 but somehwere on their way, they seem to pick up some nifty skills and talents as I saw my friend do some really cool stunts with his druid, almost as cool as I did with my shaman. He said, he leveled only in the lazorowl-specc and had some fun with that.
Warlock: I don't know... When you start off, you'll just cast some shadowbolts. Then you get your first demon and he casts along with you. Then, finally, the
VOIDWALKER! But from then on, the warlock went downhill for me...
badly! You have to be really careful not to pull aggro from your demon. Then you get OOM pretty fast, meaning you have to switch life into mana and then steal life from the mob (which costs mana again!). Then you have to heal your demon and drain life from the mobs again, because you give your life to the demon. When you drain life, it costs mana and you have to turn life into mana again and....
AAAAAAAARGH!
Leave me alone, will ya?
Rogue: If you like to play unfair, you'll probably like him. It takes a while to get the talents and skills but as soon as you've learned to keep your
enemies victims knocked out while you slice'n dice them, it starts to be some helluva funtoon. The only thing I always cursed about is that you are always tempted to go invisible and sneak past your
enemies victims instead of fighting and killing them. It so cool and you are so proud that you could pull it off until you realize... No XPs for sneaking!
I didn't play the other classes any further then level 20something, so I don't dare to talk about them...
