Lollapalooza itself could be fun (I wouldn’t know for sure, however, because I’ve never been).
Lollapalooza as an event in Grant Park and all that it brings (i.e. traffic, annoying tourists, honking horns, annoying tourists, loud music, less annoying but still somewhat annoying tourists, trash, etc.) is definitely not fun.
Good thing I don’t have to drive in the city.