When I was young , I really used to enjoy assemblies - I have a lot of happy memories just chilling with friends , working on food service , trying ( usually unsuccessfully!) to chat up young sisters. The sessions of course were long & boring but if you could get a job that involved missing some of them then it was actually quite enjoyable. I remember one particular convention when I was dating a cute pioneer sister , it was really sunny , there were lots of friends around having a fun time and it was probably some of the best few days of my life. In fact , I even went to a "listening" assembly as I enjoyed the experience so much.
As Antioch has said , there was a time when there was a lot more emphasis on being a decent Christian and you really left the assemblies feeling good & built up - I guess that kind of changed after the purge in the late 70's when the WTBTS became much more Pharisaical. Nowadays JWs kind of leave feeling that they have to do more more more for the society & feel guilty & beaten up. There was also an exciting feeling that Armageddon really was imminent which also has diminished with the passage of time.
Latterly of course other things have changed - food service was scrapped , there was a change towards purpose built indoor venues rather than the big outdoor stadiums , much shorter lunch breaks , clamping down on social events in the evening - and it wasn't really much fun any longer. The last few assemblies & conventions that I went to I honestly couldn't get away quickly enough.