It depends on what you are looking for. I'd assume all of the banks are closed, not sure about shopping or museums, but do you really want to do that on Bastille day?
I was there for Bastille day in 2006 and would go again in a heartbeat minus a few things.
+ Parade in the morning: The parade consists of military vehicles parading down the Champs Elysee. I guess even the president is involved although I did not see this.
+ Air force fly-over: We're not talking about a small formation flying over once, it seemed like every type military plane representing France in a long, loud fantastic display. We had no idea this was coming and depending on where you are situated it is very loud if you are trying to sleep in.
+ Military displays: Walking around the city we found different military vehicles parked with soldiers explaining the uses. Even if you don't speak French, it is fun to climb in the vehicles and watch the littles kids go crazy over this.
+ Fireworks!!!
+ Fire House parties: All around the city there the fire fighters (Pompiers) throw parties. Where we were it was in a giant hall with bands, dancing and food.
+ Generally everyone in the city uses the day to relax, have fun and celebrate.
Things that added a negative to our experience:
- Be careful of very small children throwing fireworks on Bastille day and the days surrounding. Maybe I'm just not used to this, but these fireworks are often not thrown with much caution to other revelers, so just keep a defensive distance.
- The fireworks started earlier than I had read and unfortunately we missed the beginning while underground. (My boyfriend repeatedly tells me I owe him a Paris fireworks display as in was my misunderstanding!) It's a good idea to get there early for a good spot anyways.
- Not so much going on right at Bastille itself. There was a small stage with a very small audience with a very large protest overshadowing it. This was during the day, maybe there is more at night?
- As with any holiday anywhere, be wary of your alcohol consumption and that of others. Walking home from celebrating we unfortunately witnessed a horrific hit and run accident. A man was hit trying to hail a cab, the car stopped just ahead to look, the passengers threw multiple bottles out of the windows and then sped off. My boyfriend luckily caught the plate number and we waited with the victim for the police and ambulance but can say it was not the happiest of endings to a great day.