I was impressed to see that the screenplay was a genuine collaboration of Hawke and Delpy with director Richard Linklater. The script was really impressive - a lot of time is spent talking about seemingly mundane details of life - work, family, recent history - and yet there's just something about everything they say that teaches them, and us, something about each other and ultimately leads to the conclusion. Which I won't give away of course. :) The ending is great. One of those endings that just feels right. Comfortable.
After watching Before Sunrise I wrote that I wasn't quite sure of it with one viewing, but predicted it would grow on me with multiple viewings. I was right - the 2nd time I watched it I felt much more connected with the characters and appreciated their stories more. Maybe I was just paying more attention.
Before Sunset (the sequel), on the other hand, I loved first time. Ethan Hawke and Julie Delpy are wonderful. The entire film is just those two, conversing as they walk around Paris. There are some truly beautiful moments when it's like you're watching a little current of energy connecting "Jesse" and "Celine" as they gradually explore one another.