I used to fare better with the three-day conventions (they haven't used the word "assembly" for three-day events for a long time) than I do now.
The downsides of the old conventions were they were often in draughty sports stadiums, open to the elements, and, for non-US attendees, every talk or drama was all American accents (apologies to US readers, but the fact is most English-speaking JWs outside the USA got sick of hearing the same accents and phrases in everything, as if there were no capable speakers from the UK, Canada, Ireland, Australia or New Zealand), and with those weird cadences and exaggerated enunciation of Bethel speakers.
But the upsides were that they seemed more like actual meet-ups of friends back then, and the talks themselves seemed more engaging and meaningful then, with more mature speakers who (usually) seemed to have life experience. Today, it all feels a lot more flat, and it's all bite-size symposium items interspersed with frequent (largely pointless) video clips, and many of the speakers are very young "corporate" types. It all seems very "lite" - like a cross between an evangelical meeting, designed just to stir emotions, and some kind of children's Sunday school, with simplistic talks and videos.
These days though, because most conventions are held in event centres, it's easier to dodge out of them and find distractions, either by volunteering for assignments, or just by leaving the seating area and spending time elsewhere like the food hall or outside seating. And many have a local broadcast of the programme, so you can tune in and listen from the car park or outside area (if you want to) while doing other things, and just tune in and out as you feel like it.
The short answer for me is, I don't think I could cope with three days of just sitting listening (or watching) anymore, as I usually use the time to be active working on assignments or doing something else while the talks are going on. That provides a distraction from the parts of the programme I really don't want to listen to, and if I'm working I can feel I'm actually being useful rather than sitting passively having that simplified stuff wash over me.