While running this, my party of 5 PCs took the encounter outside the cave fairly easily, with the Ranger hiding in the bushes and picking off 2 minions at a time before they could reach where the rest of the party fought downstream. When the skirmisher escaped into the cave however, the party began to have issues.
First, they finished dealing with the rest of the kobolds outside, and chose to wait for the reinforcements at the mouth of the waterfall. The wizard readied an Icy Terrain to trigger when the first kobold exited the cave, and killed nearly half of the minions that issued forth. Unfortunately, Irontoe had been warned and had marshaled all of his forces from the cave to assault the players. The party was overwhelmed over the next few turns, the Fighter and Warlord stood together and were flanked from almost every angle. There were enough kobolds left over to harry the Cleric, while Irontooth took on the rogue that had foolishly tried to sneak attack him.
Over the next few rounds, the Fighter and Warlord were up and down. The minions allowed the skirmishers to gain combat advantage and just wailed on the party while two dragonshields took the cleric down and Irontooth obliterated the rogue. The saving grace was the ranger who ably took down two minions at a time to lessen the incoming damage on the tanks. The party won, but only after they had exhausted every daily and had literally 2 healing surges left.
I think the point of that rambling story is that especially with more than 5 party members, KotS tends to lose a lot of the challenge factor. The only way I've seen to make it challenging is to trigger multiple encounters at once or in a sequence. For instance, when the party first entered the Keep, one of the goblins snuck off and alerted the dig site and the torture chamber, and the noise eventually alerted the goblin king. This huge encounter was extremely challenging, and I assigned an xp bonus to it, as the party defeated it without having to run away.
Frankly,if I don't cascade encounters like that, the party tends to walk over anything the keep throws at them. They're on the second level now, about 4 encounters away from Kalarel, and I think the added challenge has really made the game more interesting for all involved and we've had a blast.
-Krensus
