You'll get used to the new fighting system as you go.
I got my ass kicked a lot of times in the prologue too, but slowly got better. Remember to dodge and use your signs. I found a good strategy against multiple foes is to put down one of those trap signs (Yrden I think?) and use the protective one (Quen?). Lure the toughest opponent into the trap and kill the weakest while you're protected. And all fights get easier if you just drink Swallow beforehand and dodge a lot when your health is low.
When fighting shield-dudes, you'll need to block to catch them off-guard, which can be annoying if you've just used up all your vigor on casting signs, since you can't block when you have no vigor. Got killed a couple of times before I realized that

Bombs can be very useful too.
This post was edited by PlanHex on May 20 2011 07:49am