First, if you are going during the high season, you MUST reserve your tickets online a few days in advance. The line for unreserved tickets was at least 150 people long. Even with the reserved tickets you have a little waiting, but you will not waste an entire day standing in line for a possible spot.
Second, I really would not go here again, and I certainly would not recommend it if you have limited time. If you are interested in art history, by all means, go, but if you are just seeing the sites as an art- lay person I would leave this one out.
It was terribly disappointing. We rented the audio headset guide which turned out to be horribly boring. In addition, we had friends that went on a guided tour that lasted three hours. They were miserable after about 10 minutes. The only people that really seemed to enjoy the museum were art history students and people who had hired a private guide. The information written on the plaques (in english and italian) beside the paintings and sculptures usually gave a detailed history of when the museum aquired the piece and were it was before the museum got it. Most plaques say nothing about the painting or the painter.
In addition, many rooms have such poor lighting that you cannot see the paintings, and the walls behind the paintings are not painted to highlight them at all. Also, many paintings are behind thick plexiglass but not the modern kind that reduces glare. In those paintings, it was impossible to actually see anything but reflections of the people behind you.
There were some nice sculptures, but we have been spoiled by some of the Greek museums. The museum building itself was quite spectacular. I enjoyed the art on the ceilings and floors much more than the art they had put on the walls. There are also some very nice views of the city from the top floor.
All in all, it was not horrible, but it certainly is not worth the unreserved wait. If you can only see one museum in Florence, go to the Accademia and see the real David.