Although sometimes it's tough to discern due to complexity of Bills, I don't like Kerry's voting record in the Senate on military appropriations issues. I also think he will be much more suceptible to foreign influence in executing operations against terrorists. Subjectively, I think that's a negative. Lastly, he can't balance the budget and do all the other things he claims he's going to do both domestically and in foreign policy. Something will have to give, and I believe it will be things like NASA, Homeland Defense, and the Military (some of my top priorities).
However, I may be the only person in the US that doesn't believe this crap about "the most important election of our lifetime". I really don't think things will be significantly different no matter who is President (between these two).