Outstanding moments? Too many to list, but here we go.
The Witcher 1:
Geralt's quote about his two swords. "They're both for monsters." That line stuck, and it made me a Geralt fan for all time. Short and insightful.
Figuring out the plot about the Beast, where it came from and how all these charming people were involved. That was the moment when I realized that yes, this was exactly the type of game I wanted to play, and boy I wasn't disappointed.
The "Vizima Confidential" quest and how it did NOT insult my intelligence by feeding me more and more clues and journal entries until only one suspect remained. No, I could decide for myself and be wrong and the game could handle it!
Shani's party and how different it turns out depending on who got invited!
The last chapter and Vizima burning, and ghouls feeding on the corpses of the freshly slain in every other side street. No big speeches, no tearful announcements from some emo characters, but just an extremely effective approach of "show, don't tell". The city was going to hell, and you needed no frigging dramatic speech to know it, you saw it EVERYWHERE!
The Witcher 2:
The first step out of the tent and realizing how awesome the game looked! (Well, Triss was looking pretty awesome too just moments before).
Following King Foltest and Fitz-Oesterlen through the lines of Temerians, with the king talking to the arbalester and that scarred soldier. "Those who did that live no more!" How Foltest seemed generous to those who served him well, but a lying ruthless bastard to those who opposed him ("Surrender and you will be treated well", yeah, heh). Without any character telling me, I concluded that he was a good king... not a nice one, mind you, but a good one. Good as in "effective". And that in turn made me care about his death, no emo crap required.
Roche and Iorveth. Both flawed characters and yet likeable. I have a hard time deciding who to side with every time I play, and that's saying something. It's the complete opposite of some other game released in the same year as TW2, where I really really didn't want to join any side but frigging HAD TO!
The moment where Geralt meets his friend again in the tavern. That first big conversation is a favorite moment, simply because I like the atmosphere and dialogues so much. Zoltan's tale of his failed marriage cracks me up every time.
Finding out how different Chapter 2 turns out depending on who you side with. That was an utter jaw-dropper.
The conversations with the surviving veterans and the ghosts of veterans of chapter 2. Usually, the word "visitor" is a rather harmless one, but those conversations made me associate it with something really terrible.
Letho. Vodka. Enough said.
The artbook from the collector's edition was awesome. It truly opened my eyes about how much care and love had been put into the design of the game. Needless to say, my next play-through was a lot slower and with a lot more looking at all the details. No one should just rush into Foltest's siege tower without giving the whole thing a good look first. It deserves it.
Generally, Geralt as a character and his dialogue work incredibly well for me. Whenever I see the possible replies he can give, there's pretty much every time something that fits exactly my thoughts about the situation and I just go with instinct and gut-feeling instead of pondering how which choice may affect some morality meter. Feels very natural.
The way the games handle conflict, character motivation and such. Kudos.