WoW's pretty fun. I don't think we can describe to you the feeling of each class and their differences easily, you'd have to try them out yourself.
(to answer your ranged dmg/healer)
I play a druid, and always had since release since I though shifting was pretty cool. Hybrids are paladin, shaman and druid. Out of those 3, two(shaman and druid) can do ranged damage and heal depending on what you use your
talent points to specialize them in.
edit: forgot warlocks can drain health too if you like that
For example,
shaman will have these:
- Restoration, healing
- Elemental, ranged magic damage
- Enhancement, melee fighting
And basically you have points to put in there and specialize in each area... All classes have 3 trees, so it's kind of hard to just tell the overall difference of classes.
I think you already know what I just said but I wanted to just let you know for sure! xD
(the three classes you listed)
MAGE:
I love mages, they can make food so you don't have to buy any xP
They are more of a burst DPS class than warlock, generally, because they have less damage over time spells. Warlock can still burst just like the mage if specced destruction though. Mages have alot of tricks such as blink, ice block, frost nova, polymorph, and counterspell. I like mage!

They have minor mana problems though, but with changes to evocation, it shouldn't be bad at all. Mages have the most Area of Effect spells.
WARLOCK:
These guys have the PETS mang! the pets will be like your utility, each one will have a special move for certain kinds of fights. One can silence, one can tank, one can seduce, immobilizing enemy, etc. The warlocks have more DOTs than mages but if you want to do more bursty damage instead of over time, spec destruction. Life tap, transferring life to mana is great, it's why warlocks can keep fighting at the cost of their health. You can drain health from your enemies too.
HUNTER:
These guys can track people on their mini map. They're basically clothie killers (Ithink) lol. Their arrows hurt alot and when you let them stay faraway, you're sure to die unless you can get close to them. As a hunter, you'll be kiting because you can only have your fullest potential at shooting range. Both other classes also have to kite too though, but if a hunter vs. mage, the mage would want to close up onto the hunter to not let him shoot. They're pretty funny because they can fake their deaths and put down traps to freeze enemies/burn them.
Although all classes have multiple things they can do, all of them have different play styles.
Uh. I hope I didn't just list the basics that you already know. But there you go!