Well, he's not entirely an empty suit, but there isn't much interest in what he did while he was an IL legislator. In any event, CQPolitics has taken the liberty of comparing his voting record with some of the other Presidential hopefuls. The idea is that you have a general idea of where Clinton or Edwards sit, so you can get a feel for Obama by seeing where they were different. They even include excel sheets giving the bills where the votes differed.
Of course, you'll probably have to look up what the significance of each vote was. It's pretty hard to know why someone voted the way they did when only the name of the bill is given. Still, this goes quite a ways towards giving a solid definition of who Barack Obama the US Senator is.
Of course, you could always just let the man speak for himself, too.