Collaborative creativity is one of my favorite things in the whole wide world, and being at the table with other gamers creating a stories and thereby worlds in real time is one really exciting way to do that. PbP has less immediacy, but scratches different areas of that same itch.
I like real-time, immediate problem-solving. It's very satisfying and I'm pretty good at it, and gaming usually provides a steady stream of problems to be solved. My ADD brain loves it.
Social. Most weeks, the gaming table is my only big social interaction outside of work and family.