Well if anything, after learning more about Olgierd, heart of stone or not, I found his actions to be as despicable if not more than Gaunter O'Dim. While he's lost the ability to feel emotions (similar to witchers), he still has the ability to think rationally and he's made some really evil decisions. I really wanted to kill him so I was really hoping even if you decide to save Olgierd, he will show his dark side and try to kill Geralt, leading to a final showdown
I would just like to point out, as I have seen a surprising amount of people make the same mistake. The thing about Witchers being stripped of their emotions is pure poppycock, drivel, shite and eight other varieties of nonsense. It is hate-propaganda spread by those who hate witchers.
Geralt and the other witchers don't bother pointing it out because most people wouldn't believe them, and in fact it sometimes works in their favour.
The closest it comes to being true is that because witchers go through a ton of harrowing experiences and witness the lowest depths of depravity in humans on a daily basis, as well as being hated pretty much anywhere they go, they become quite hardened and cynical over time.
Their emotional capacity as humans however, is entirely intact. This should be obvious from the emotions Geralt goes through in the books and games.
On topic though: Yes, Gaunter O'Dimm was an excellent villain. I guessed he was in fact THE Devil as soon as he told me to meet him at a crossroads.