Most people seem to say it's boring, but I 100% disagree. All of us have seen dozens of fireworks shows from the ground. They're basically all the same. I tend to get bored well before the end of the show.
But I've gone on fireworks flights a few times, and even my passengers have thought it was a really cool experience. Yes, of course you can't hear them, and they look smaller. But so does everything, and we are always marveling about how amazing the view is when we're flying, so this isn't any different. Obviously it depends on where you live, but you can see multiple shows at once and it's fun to figure out which show they are. No, you wouldn't want to just circle around and watch the whole show, that would be boring indeed. But flying from show to show, doing a quick lap maybe? I think it's great.
Even better is if you live somewhere where fireworks are legal and available for the general public. Around here, where fireworks are easily available (and sometimes even legal) in many towns, flying overhead is really neat - it's like a non-stop WW2 bomber movie, just the flak below you is fun and colorful. Everybody with a driveway seems to have their own show - and these aren't just sparklers either, people put thousands of dollars into their home shows and buy some serious hardware.
One town near us (Mustang) actually opens up the park for a giant free-for-all, launch-what-you-brought party, with the fire department standing by. For the whole week prior, school sports teams and clubs sell fireworks for fundraisers, and then are responsible to clean up the park (to ensure a booth the next year). It's wild. And great. And flying over it is amazing.