Have been thinking about it some more.
Trolls are designed to be annoyance. All civs are at war with them (including barbarian trait leaders), they heal as quickly as other barbs (and that means standard rate but also while moving) and are quite common.
Maybe even too common.
I do not want to remove them, nor change the way troll caves work - these are designed to be annoying, too. And as I recently explained in another thread, I want swamps to be dangerous even within your own borders - until you drain them, that is.
So I see two possible solutions (or any combination of the two):
1. Tone down troll numbers
troll caves have spawn at once limit at 3 now. One guards the lair, the other two do the sightburning. It can be easily limited to 2 at once, with only one wandering.
Of course, it is the max cap. If there is active troll killer around, there are less than 3 per lair.
2. Reduce base strength
Trolls are strength 4 unit with double swamp movement, swamp combat bonuses and mountain climbing. Also heal while moving.
So, before you have hunters (which gain +50% against trolls and other beasts/animals) or any good tier 2 attacker, it is quite hard to kill them.
So, maybe I should reduce their stregth to 3, but introduce i.e. mountain troll (bigger, gray coulour

) with base strength 6, but requiring barbrs to have certain tech - thus spawning later. Also, all standard trolls would upgrade for free barbs get that tech. The question is, what tech should in be?
Also, to make them more trollish, I might add a trollkin promotion that allows even captured trolls to heal while moving, grants big healing bonuses and healing after combat.
So, what do you think?
If you prefer to keep it as it is, please voice your opinion too. Or if you have another suggestion.