I just finished the first season and I really liked it. The animation and sounds were great. Furthermore, you quickly learn to like and respect the main character, Ryouta. Also, the subplots/action events were well laid out. The characters' back stories (when they existed) were great too. So I'll deem this a great overall story, so far. Hopefully the surviving characters can make this a little more interesting.
Things I didn't like, but I'll accept, are the simplicity of the most remaining secondary characters/antagonists. I felt as if they could've gone into more depth with them. I can see how they wanted the audience to accept that they were bad people with bad intentions, but I know that's bullshit. Everyone has a story to tell -- so they shouldn't've rushed their deaths.
Secondly, I'm not a big fan of seeing girls as stupid, secondary characters in a show. The story could've been made slightly better had they made Himiko (and other females characters) more important, and not as dumb.
Overall, it's a great watch. I'd recommend Kaiji for those those who felt the story was great and can live with boobs not flying everywhere.