I'm probably one of the few people still digging this series. It's not as good as the show, but as far as an adaptation of something from another media, it's definitely one of the best.
That said, I've been waiting for YEARS for them to reveal who Twilight is. I thought it was going to be Riley until he appeared again. Honestly, the longer it's stretched out, the more anti-climactic the reveal is going to be.
Right now, my money is on Caleb, but the options for who it could be are running thin. Possibly Giles; that would be a great switch. I could see him being entirely against the idea of a Slayer Army.