Dave - your CV basically gets you an interview, beyond that it's how you perform at interview, how you interact and how you perform in the case studies that determines whether you make it through and secure an offer. I would bet a fair amount that it was your interview performance that cost you the job first time round.
Most firms will take the view that a graduate can have developed and matured quite a bit in the year after leaving University, so you're unlikely to be automatically rejected simply because you didn't get an offer in the previous graduate intake year. As before, you'll probably get a number of interviews and it'll then be your interview performance that determines whether you make it through or not.
As an aside, I would also consider approaching the 3 firms that you got to final rounds with and seeing if they'd like to have you in again for interview now (rather than waiting for the next milkround process). Given the hiring difficulties and staff attrition that many firms are facing right now, they might view someone who they almost made an offer to last year as an attractive hiring proposition... Just a thought.