I'm trying to descide on rolling a troll shaman or Druid, I have a level 40 Druid so i know what they can do, so what do shamans do, and what class should I roll?

Shamans can fill three different roles:

Healer(Resto Talent Tree)
Melee DPS(Enhancment Tree)
Ranged Spell DPS(Elemental Tree)

All three have different totems they can use to help support groups with different buffs.

What you should roll depends on what role you would like to fill.

If you are looking for a good DPS class my personal favorite is a Death Knight, which should become available to you at level 50.

Hmm.. I'd say Shaman because they can be a "Mage" a "healer" or even "melée dps"

Well if you've already played a druid (and got bored before reaching level 85) maybe try a shaman? Really when you play WOW you need to find YOUR class. One that you enjoy more than the others, mine personally is a warrior, although most people find them very basic and boring, I think they're the best class xD Try different classes and find your favourite