Kayran fight is bit tricky, but this video should help (it also shows the location where you need to go). You will need to use the trap spell against the tentacles, and then at last part climb on to the rock to reach the center of the creature. After that part the game is mostly very much fun, it´s just the prologue and Kayran being bit glitchy at times that can piss off people.
https://www.youtube.com/watch?v=oschdW3HKUs
I never understood how people find Kayran tricky. I mean I am not very good at games in general and in Witcher I usually get my ass handed to me even on normal difficulty setting, but FFS the Kayran battle is easy. Pick a spot in front of the big tentacles, set a trap spell on ground, wait until the big tentacle readies itself for attack, roll to the side, attack the big fricking glowing thing in the tentacle that almost has a "HIT THIS" sign on it until it breaks. Rinse and repeat couple of times. Then run up pillar that fell on top of the Kayran and boom he is dead.
Well, unless you have QTEs enabled then you have an unfair "hit X to not die" moment after that but thats your fault for keeping those stupids QTE enabled.
Anyone having problems with gameplay use a Xbox360 controller. To be honest the game was designed around that. Then it plays a bit like Batman games, just slower and with harder hits.