Story: For a story that consisted of several parts and characters, it came together very well. All the pieces fit together that kept you guessing until the last moment. There weren't several loose ends (even shows with a few characters, one plot, and 20+ episodes can't pull this off) and left you wanting more only because the journey was so great that you want to do it all over again. Baccano! tells it's story with style and plenty of humour. I wasn't expecting to be laughing so much and enjoying the story as much as I did (I don't do well with complicated stories because I become confused easily). Baccano! simply has it made. It has intelligence, style, humour, action and drama with a supernatural twist. As long as you can stomach some violence, I would recommend watching this.
Animation: The character designs were lovely. They fit the time period and were memorable. It's hard to forget Isaac and Miria. The backgrounds were perfect and the action scenes were enticing. The opening sequence is one of my favorites although the ending was bland. However, my main complaint with the animation were some sequences when it was dark. Obviously something important happened but you just can't seem to make it out. I don't know if it was censored or if my screen had a glare, but I could hardly tell what was happening. However, it doesn't happen too frequently and you still get a jist of the story.
Sound: Wonderful soundtrack. I'm on the verge of buying it. If you like jazz, plan on falling in love with this soundtrack. Also, the opening and ending were great although the ending lacked some fun. The seiyuus were terrific. The voices were perfect. I have no complaints about the sound.
Characters: I have trouble remembering a large group of characters if they don't have presence. I have seen series where I can't remember a single person's name because there are so many of them and they don't stick out to me. However, Baccano! wasn't the cause. I could remember almost everybody's name within a couple of episodes (definitely before half way). They are an interesting bunch that stick with you and ending up being related to each other in the strangest way. However, Baccano! does less character development but more of further explaining the character. They don't change but you get to know more about them and their relationships with other. Some were a little bland (Lau and Berga for example). However, the rest make up for the other's shortcoming. My favorite were Isaac and Miria. Never will you find a more likable couple.
Overall: There are little series out there like this. It will definitely take you on a fantastic journey full of laughs and brains as long as you prepared for some violence. At the very least, go listen to the soundtrack, fall in love, and then watch the series to fall in love again. This is definitely a series that I will put on my favorite anime list and one that I would rewatch.