Full description of bloodthirst:

Benefits:
Strength Restoration: +10 or so at level 40, FULL strength recover even at -50 at level 51.
Disease offset: Plague, Poison, Rot, will all be delayed in working. The timer won't tick down, but it won't be in effect while you're under bloodthirst. This is a good way to buy a extra couple hours.
Mage in area: Can bloodthirst outside of combat.
Thirst off a friend: Say you're stuck with no movement about 4 steps from the Destructor and you're going to die in the last 2-3 ticks. Get a friend to thirst off and walk to the shrine.
Negative movement: Bloodthirst lets you go into negative movement, super clutch when you're a sword spec low on moves and a big fight pops off at the Village.
Damage increase: +15/+15 Flat increase to hit/dam.
Hastening effect: Thirst will hasten you. But it will not take you from slow to haste or even slow to normal speed. Against a transmuter always haste before he can land a slow.

Drawbacks:
Extremely shitty HP regen while under fatigue.
Fatigue acts .like slow, so your melee is heavily weakened
Autoattack everything: Summoners can fuck with you real nicely. Thats the biggest drawback to thirst. Regen forms can also fuck with you nicely if you take a bad fight way in the middle of nowhere.
Must wait until fatigue is finished before re-thirsting.
Hunger/Thirst increase rapidly. Try and eat/drink right before thirsting.
You can't eat food, but can drink water, ragers have died from taking hunger damage as thirst wore off and are at critical HP.

Thats about everything off the top of my head. A rager that knows how to use b-thirst as an advantage, will significantly find more pks.