Kill Bill 2 was much better than the first.
Here's how the movies break down. Vol. 1 is about The Bride setting off on her quest o' vengeance. Sounds good on paper, and I liked the movie, but it's a rocky start because there aren't tons of tense moments, surprises, or bits of character development, and those things are basically Tarantino's trademarks. Ultimately it comes off a little flat for most people.
Vol. 2 is all payoff. There are some very tense moments and there's much more emphasis on the characters. I mean, this is still a movie about international assassins, not a character study, but within that context they are developed as much as I could have wanted. The fights are better-staged, and resolve in interesting ways.
I would say that strictly speaking you don't have to see Vol. 1. In fact, there's a big plot twist in Vol. 2 which might work better if you haven't seen the first.
So, I thought it was great. I'm excited to see it again. (My mom looks kindly upon Quentin Tarantino because she loved going to Video Archives back in the day. So I always see Tarantino's movies in the theater with her.)