I think the primary reason is that he's seen as the best candidate to beat Bush - the polls are showing them neck & neck according to the radio this morning.
Here's his official website bio:
http://www.johnkerry.com/about/
The rhetoric is basically standard middle of the road Democrat - you can navigate to it from the site above. Some interesting pieces are the support for the same rights for civil unions as marriages (which is an interesting dodge to that issue), and the requirement to have all high schoolers perform community service to graduate (hmm.. education is a STATE issue according to the constitution...). Cut the budget deficit in 1/2 in 2 years.... increase funding for all sorts of programs...
Cynical? Who? Me?
... Vote Cthulu - why settle for the *Lesser* of the Evils? ....