Paris is really beautiful and has some amazing attractions for tourists (the Eiffel Tower, Notre Dame, the Louvre, the Champs Élysées, the Sacré-Coeur, a cruise on the Seine etc. etc.). Versailles is outside Paris but it's just a train ride away and well worth a visit. If you have kids, there's the added appeal of Disneyland Paris. There's history, architecture, art, fashion, romance, good food - what's not to like?
The first time I visited (almost 30 years ago), it was fairly easy to visit everything. We pretty much turned up, paid our entry fee and walked in. I visited again a few years back and there were massive queues for everything, which took away from our enjoyment. You'd probably need to pre-book everything now. Having said that, the first time we went was October and the second time was June, so maybe it's just a lot busier in the summer.
Paris is divided into different districts called arrondissements. Some of them are nicer than others. A quick google will show you the arrondissements and a bit of information about them.
You need to have your wits about you, same as any big city. There are hagglers in some areas and they can be quite aggressive. I saw a guy pull a knife out of a backpack near the Metro at Sacré-Coeur, which was pretty scary.
If I ever go back to Paris, I'm going to skip the attractions and just enjoy the city - bars, cafes, shops, parks, food markets etc. Lots of walking but no queues.