Any quest I tried I can't kill the monsters. I healed one of the 2 soldiers in Aleroth (using that orb), but I didn't get a reward for it.

I know a single orc slaughtering an entire camp is hard to believe, so I recorded it on twitch:
http://www.twitch.tv/boe2/b/397745395

First there is some confusion because I accidently get the attention of a boar and a spider as well.
Around 0:50, notice how much trouble the guards and me are having killing that single spider
Around 1:22 the elite orc finds his way in, and...well...goodbye barracks.