Can't give much in the way of pure Vanilla notes, so expect some BC bleedover. Also can't account for any changes or adjustments Fishie may have made~
Rogue: There are builds that can generate a surprisingly high amount of damage with poor gear at the expense of not scaling all that well as gear improves, so still capable of laying on the hurt if one of the less gear-centric choices are taken. Also still Vanilla, so
"Balance" may still be in effect.
Edit: Can also engage in low-risk fundraising by stealthing around camps of hostile humanoids and picking every pocket in sight. Lockpicking really can come in handy. Traps are rare, but it's Fishie, so you never know~
Warrior:
Utterly, totally gear dependent. I
cannot stress this enough. Once you actually
get that gear, though, you're basically impossible to kill so long as you have a functioning healer. Best at tanking bosses by a mile, has a hard time keeping groups tied up. Damage is also pretty decent, if you go that way, though not as good as the Rogue's (again, gear gear gear)
Priest: Buffs and Big Meaty Heals, out of battle resurrection, Shadow Form and accompanying spells hit fairly hard and leech health and mana to your party.
Hunter: Pets have the life expectancy of a snowflake on the surface of the sun in large group content. Oh, and leave them on passive or you'l-
YOUR PET JUST PULLED THE *ENTIRE*
INSTANCE WHAT DID I TELL YOU ABOUT LEAVING IT ON PASSIVE
*ahem*
You shoot the mans at range until they fall down. One of your bag slots is dedicated ammo storage, to which you will feed a fair portion of your funds in an attempt to sate it's ravenous hunger. They eventually do away with both quivers and ammo, but that's not for a long while yet.
Druid: You do everything, but you also suck at everything. Except healing, you're pretty good at that, and you fill a different niche than the Priest so there's not much conflict there. You also get an in-battle res. Once BC hits, you actually become pretty good at whatever you feel like speccing towards, though not to the degree of the more focused classes(Again, you have your own little niche on healing, so you're still sitting pretty there).
... Meh, on a roll. For classes we
don't have access to:
Paladin: More Big Meaty Heals. Also a lot of defensive stuff. As the old joke goes 'If you want to kill a Paladin, you need two people; one to fight him, one to wait in Goldshire to jump him after the Bubblehearth.' Not as good as a Warrior for boss tanking, but is
excellent at keeping large groups of weaker foes focused on them. Damage.... basically doesn't exist outside of gimmicks.
Mage: Great damage up until BC hits, whereupon Blizzard overcorrects for a specific gimmick and nerfs the class into the ground so hard
the crater is visible from space. One or two will still be brought along as living vending machines. Most of their class-specific gear has most of it's itemization wasted on Spirit, which is literally worthless for them. Will likely take their pain out on others by playing Portal Roulette.
Until 2.3 hits, whereupon they become unstoppable killing machines until WotLK actually hits, but that's a long ways off yet.
Warlocks:
Vanilla: Overpowered
BC:
Horrifyingly Overpowered.
ALL OF MY HATE
*ahem*
Not bitter at all, I assure you.
Shaman: They do supporty stuff. Kinda like a Druid, but less form shifting and more Lightning and Totems and Bloodlust. Horde-only until BC hits.