Update on my (first) run so far: I killed Tartuk and the troll leader Hargulka, with a party of level 6 characters, and none of them died. But I had to reload several times in order to pull that off. This was an insane fight. Hargulka has some crazy stats. To give an idea, Charname has 19 Strength and Valerie has 19 Constitution, they're the tanks. But Hargulka has 33 Strength, 22 Dexterity, and 33 Constitution (!). On top of that, after Tartuk casts Haste, Hargulka can attack
up to six times per turn. He can actually kill a tank like Valerie in just one turn.
After getting crushed a few times, I had to step back and think "Ok, what's my strategy here?". I started trying to connect the dots, like "Ok, I'll have Linzi start this by casting Fascinate. Then I'll have Harrim cast Touch of Chaos on the troll leader, then Linzi will cast Hideous Laughter. After that, I should have Octavia cast Reduce Person. On Harrim's next turn, I'll have to lower his stats with a Curse spell. Etc., etc."
Fortunately, that strategy ended up working. And the need to come up with a strategy is one of the things that I'm really liking about this game. I've read some comments by other people that said that buffing the party before combat is the way to go. In games like Baldur's Gate 2, that's what I usually do, and I also like to summon as many creatures as I can. But in Pathfinder: Kingmaker, things seem to be different. First of all, Summon Monster I and II gives you some creatures, but you don't directly control them, the AI does. So I don't use summons in this game. And, honestly, I don't buff up the party before a tough fight, because I don't really have a lot of buffing spells to begin with. Sure, there's a few ones that can give you a little bit of an increase in this or that stat, but it's not like in Baldur's Gate 2, where you usually cast like 10 different buffs before the fight. Here it seems that the focus should be on strategy, finding out which combinations of spells are the right ones for a particular situation. Even the order of turns makes a huge difference. Even after rolling Initiative, I micromanage the order of turns of my characters (you can delay the turn of any character in your party, so you can decide who goes first, who goes second, etc.)
It's a really great game. I'm also liking the kingdom management part. My barony isn't much for now, but I'm working on it : P
On a side note, the way that Harrim's story kept developing in the Troll lair was very interesting.