My only cruise I've been on was on an old crappy Carnival cruise a few years ago. It was the boat that caught on fire while it was out to sea like 2 weeks after I got off it. I barely saw any people my age, and didn't meet a single person. I hung out with no one except once in a while walked around with my sister. I could find nothing to do on the ship except play in the arcade; there was a comedian one night and i did enjoy that. The sport's deck was just an open area where you could throw a ball or something--I was hoping for a basketball court or something and was really disappointed. I was so bored that I basically just napped the whole time. When I woke up I'd just go wander around by myself for a while and eat pizza(I ate a LOT of pizza that cruise).
I enjoyed the ports much more than I enjoyed the ship. There were great moments and I did have some fun...I just know my upcoming cruise is going to be much better.