I'm really enjoying grappling. I'm signed up to take it twice a week, though for the next few weeks some travel will interfere with that plan.
What I enjoy most is when I get paired up with a young guy--late teens or 20s--who doesn't have grappling down yet. He's totally trying to use his strength, instead of technique, so he gets exhausted. I'm waiting for him to make a mistake and then I move into a good position. It's just so much fun to be grappling with a 20-something and have him gassed before me.
Of course, when I encounter a 20-something who knows grappling, or was a wrestler, I'm totally out of luck. I know some things well about grappling, but there's a lot I need to learn, and of course an athletic 20-something is stronger and better conditioned than me.
For now I'm still staying away from kickboxing. It's the riskiest thing for my knee to kickbox, and I passed that part of my black belt test anyway. My sensei is fine with that for now.