I've sat down with Gangs three times over the years. I've always thought it had great moments, but I never finish the film thinking wow. I think the plot is the most annoying part of the film. The whole love story/Bill's daughter thing... whatever. An DiCaprio's snivelling, sadsack friend. I could do without both of those characters. The setting is amazing. The look and feel and most of the characters are all really rich. ... there are movies in my top 100 with that basic plot... Maybe it's Di Caprio's character's witlessness that makes him hard to get behind.
Still, it's worth at least 1 viewing, and it won't fail to grab your attention immediately.