Story: I'm a fan of the vampire genre but it can become overdone. However, Karin adds a nice fresh twist to it (and a funny one at it). It may not make the most amount of sense but it still interesting. I really enjoyed this romantic comedy. It had plenty of romance, humor and plot twist to keep it going. The pacing was good. Not too fast but things didn't drag on too much either. Each plot line was developed and concluding nicely. You are left with a few questions but not too many. The romance wasn't shallow and the humor was hilarious. Any shoujo fan would love this. The battle was a little anticlimactic but not too much. However, the ending is VERY BITTERSWEET. Not expect things in the end to be a happily every after. I almost wanted to cry. However, it does have a hopeful feel to it.
Art: The characters looked really chunky and blocky. I was pretty disappointed. Even the bishounens weren't incredibly good looking. The funny scenes were done great and the art added to it. The character designs weren't as attractive as they could be but it didn't take away that much. They looked cute for the most part. The dramatic scenes didn't flow the best but the message still came across. I still gasped, awed, and laughed. However, the art is one of my least favorite parts about Karin because it doesn't really improve. It just remains the same throughout the series. At least it's consistent.
Characters: I loved the cast. I don't meet shoujo female leads that I like to often so Karin did a good with that. Karin is sweet lovable girl. She's not shallow and although she may not make the smartest decisions, you don't get annoyed at her. Karin's family is hilarious. I love them. They're all lovable even if they are weird. Usui is great too. He's not shallow either and his ethic is really admirable. Also, you see the development of the characters and their relationships. You really see how much they love each other. Some may be a little cliche but those are usually the minor characters. I found them memorable, kooky, and just so lovable.
Overall: A great read for shoujo lovers. The art may not be the greatest but it's easy to overcome. The characters really do shine through. It full of cute and funny moments and pretty addicting too.