Hmm. Most memorable? Well for pure shock value, I didn't see (ep. 3 spoiler ahead) Katjaa's suicide coming.
But for greatest moments that I'll love? (ep. 2 spoiler ahead) If you choose to kill Andy, and you choose to do so with your gun. That moment when Lee turns and shoots Andy dead... "I said. It's. OVER!!" *BANG*. I got goosebumps. No lie.