They started with the the director coming out and showing a clip of the boys talking at the table from issue one. The next clip was Kick-Ass confronting two guys trying to steal a car.In the book they are spray painting, and there were three. The clip to me worked out better than in the book. The third clip is Hit-Girl and Big Daddy training her how to take a bullet. My big complaint about the way the movie looks is it looks like more comedy than anything else. Yes, the book is funny, but they made it more comedy than anything doesn't fit.
The next clip was Kick-Ass going to the gangster's place and telling him not to mess with the girl anymore. He is then attacked and saved by Hit-Girl.If you are a fan of the book: yes there is blood, and yes, it looks good. But she doesn't slice people up as much as in the book.
Last they showed a comic-con trailer for the movie that made it look amazing. It was shown twice. I didn't like that they ruin something from one of the upcoming issues of the book. so I know a bit that's going to happen.(It's nothing you couldn't guess though.)
Mark Millar also talked about how Kick-Ass was going to have three mini-series and hopefully three movies. If all three books do well, they will turn it into an ongoing series.