IMO FCR makes you play The Witcher as it was originally intended. In vanilla you could just put everything into strength and strong style and then decimate everything without any oils or tactics. Now, rubedo swallow, nigredo blizzard and albedo tawny oil are my basic all-around potions. Rubedo, albedo, nigredo? Before FCR I didn't even noticed them. People install FCR and then expect to just click on things without any thought like in vanilla game.

Currently I'm at the beginning of act III while playing on the highest FCR setting and the only frustrating fight I had so far was the haunted house in act II which had 2 wraiths on one floor, 2 graveirs in the basement and little room for maneuverability, but it was still doable after some attempts. I doubt he would release this mod if the endurance tree didn't work. Apart from fighting level 50 Flash I was never stunlocked to death so apparently resistances DO work. As long as you keep using proper items (oils, potions, styles) and keep enemies in front of you you'll be good. I'm currently during my second FCR playthrough and I didn't encounter a single instance where enemy would score a hit on me while being far away. Also Flash discovered that Geralt's stun immunity (from talents/potions) doesn't work in-game, yet left the chance for creatures to stun Geralt in there, and with their ridiculously amped-up powers they can stun Geralt and then one-shot him. In particular the tendency for enemies to score hits when they are actually far away from Geralt.

I say this last point because it makes certain flaws in the game much much worse rather than fixing them. Bengeddes: (.) prepare to die all the time in frustrating ways.

Witcher 2 full combat rebalance