We went to Philly to see King Tut in Feb., DS 12, DD 10, DD 8. We spent the extra $7 (ish) for the audio tour. It really helped to explain many of the artifacts and keep up momentum. I would say to buy tickets in advance so you can get a good time. We went just after lunch. Lunch at the Franklin Inst. was crazy. Not enough tables and not great food either. Better to go outside and buy a hotdog.
As for the exhibit, you get your time to show up but then we had to wait about 30 min standing in line seeing nothing. Finally, there was a short intro movie and then you are on your own to see the exhibit which it separated into rooms. The best stuff is in the last room and by then we had been standing/walking for about 2 hours with no breaks. Nothing to drink, in a hot (due to large crowds), dark, exhibit. The exit leads to a gift shop with a lot of great stuff but it was so crowed we just left and went to the main gift shop later which was not as good. I would recommend braving the crowds if you want to get a King Tut souvenior.
I also agree that the IMAX movie was great! In fact, the whole Franklin Inst. was great! We spent the whole day there and the kids would have spent longer but it was closing.
We also took the trolley tour but the duck tour is better. (it was closed in feb.) The liberty bell (free) and liberty hall (pre-buy time slot for 1.50 online) was great. We also saw the mint (self guided and free but no cameras allowed and no lockers). The trolley will pick you up and drop you off at your hotel. It is easy to get around Philly and there was so much to see and do we want to go back when we can spend more time.
Hope this helps!