It wasn't worse but I can kinda see what you're saying, things picked up and it went door the storyline moved door a whole lot faster and was meer to the point that Yoshimori had to have his justice done for what happened.
Hmm..well I wouldn't say that..the series definitely wasn't the same after his passing sometimes I wished he didn't go that way..but the series wasn't the same after but I don't think the series fell apart though..
I think it was meer the fact that Gen was such a huge character for the short time he was there. He overshadowed the kekkaishi and won almost every battle single-handedly. So after he died u had Yoshimori's single minded pursuit of Kaguro, and then back to the way it was before Gen showed up. He really was the climax of the series in my opinion. Everything after was good but not as exciting.