Well i don't know anything about any of the classes i do want to play a spellcaster, not sure what faction yet.
My download is at 70%. I have to go to work briefly to finish off a few items, but I will likely get a chance to play today.
What are the healing classes like?
Don't worry about faction. The classes are for the most part mirrors for each faction: role-wise and mechanics-wise with exceptions. (Andexcluding balance)
So
Tanks:
Swordmaster = Black Guard => "Combo" mechanic (opening attack, middle attack, finisher)
Knight of the Burning Sun = Chosen => Uses auras.
Ironbreakers = Black Guards => "Grudge"/"Hate" system, like WoW's Warrior's "Rage." Both classes gain on their Grudge or meters when they are hit. However, Ironbreakers also gain Grudge if someone hurts their defensive target (you can target and "Guard" a friendly player). On the other hand, Black Guards are more simple and gain "Hate" by attacking.
Melee Deeps:
Witch Hunter = Witch Elf => Can stealth but it only lasts something like 20 seconds, has no survivability, but can assassinate the crap out of almost anything non-tanky.
White Lions = Marauders => "Medium" infantry in role, mechanics don't really mirror though. White Lions use a pet (mirroring the Squig Herder) and Marauders have multiple stances (mirroring the Shadow Warrior).
Slayers = Choppa => Build up angerness (Berserk/Frenzy), then either you go super berserk which makes you kamikaze, or you can keep it "under control" and be "regular" melee guy.
Healers (or Support):
Warrior Priests = Disciples of Khaine => Well armored melee hybrids that build up healing energy by smacking people, which then lets you heal.
Rune Priests = Zealots => Healers/buffers/debuffers/dps support.
Archmages = Shamans => Mechanic that makes causing damage increase their healing power and vice versa. However can use talent trees to focus on healing, deeps, or hybrid mechanic.
Ranged Deeps:
Shadow Warriors = Squig Herders => Skirmisher archer role. Mobile and survivable. However, as above, mechanics differences.
Engineer = Magus => Turrety classes. Good damage, good survivability, but not very mobile.
Bright Wizards = Sorcerers => Glass cannon major deeps.
In other words just pick a faction so I can make my damn character.