Everything. 
Well... characters, plot, and writer's block are the big three right now, but last year that wasn't the case since I had a pretty good idea of what I was going for. I think of writer's block as simply stumbling on one of the others, and thus not knowing what to write, less than running out of willpower, so I'm not sure how applicable that is to me, though I suppose my willpower was severely strained last year. Now sure how that would play out if I tried to do it again.
Well... characters, plot, and writer's block are the big three right now, but last year that wasn't the case since I had a pretty good idea of what I was going for. I think of writer's block as simply stumbling on one of the others, and thus not knowing what to write, less than running out of willpower, so I'm not sure how applicable that is to me, though I suppose my willpower was severely strained last year. Now sure how that would play out if I tried to do it again.