It's been a while since I was at one of those things--I was 10 years old (I'm 28 going on 29 now)--but I'll try to help you out here.
Assemblies and conventions of Jehovah's Witnesses are essentially extensions of meetings, except with more people, since members from many congregations gather in one place, and they last for at least 2 days. I remember seeing skits, sometimes involving costumes (if stories from Biblical 'history' were being re-enacted), and listening to tape recordings. But the point of assemblies, and conventions, is that of meetings--to keep up the mind control.
I hope this helps even a little bit, but, if not, I'm sorry I couldn't have been more helpful. Like I said, it's been a while.