It really depends. In the areas around where the big urban Fourth of July events are being held, or places like theme parks, it is likely to be pretty crazy. Beaches and parks will probably be pretty busy. Most businesses will be closed (including a lot of restaurants) or have limited hours, although tourist areas will probably have more open. On the other hand, traffic is likely to be a lot better than usual in areas where people would normally be commuting. If there's somewhere you want to go that's open but not holiday themed, there's a good chance it will be calmer than usual.
If I had the opportunity and were a tourist to the US, I would look around for a smaller city's Fourth of July celebration. Those are the really fun ones, with the local parades, and sometimes there are other festival-type activities. The big city events are glitzy, but more typical of professionally run festivals everywhere. The smaller cities would give you a taste of typical America. And most every community has some kind of fireworks show!