When fighting Trolls, use the cave entrance for cover,. Or use tall stones and keep moving around them, as you take arrow shots at the troll,.
When fighting the minions you can stand on top of tall stones, and shoot at them. any higher ground is better against them,. I use a mase and just nail them.
When inside the burial chambers use a stagbreaker, stand infront of the doors and use it, dont open the doors. the blast hit will injure anything on the other side of the doors. ,.
And yes as you beat bosses it releases more difficult levels of creatures and higher level ones. I have TWO Star trolls and draugers, plus wait for you to find an Abomination in swamps,, exciting stuff , HINT,: you can get Trolls to fight other big creatures.