Above is one of the pictures I took of the Mona Lisa... and there were not a lot of people in the room.
Don't get me wrong, there were a lot of people there, but there were no long lines. I bought my ticket and walked in. My plan was just to wander around the museum. That's what I did. Here are my hints for a hassle free visit to the Louvre. Go in an off season. Visit on a week day rather then a weekend. Be there in the morning when it opens, the earlier the better. Have a good map, I bought a detailed book - it was well worth the money. And, most important, plan on spending the entire day there. I did. If the only reason you go is to see one painting, you're going for the wrong reason and you're most likely going to end up being disappointed.