Oo Egypt is a great country to visit!
Though I have noticed that there are MAJOR problems with backpacking around...for starters, to go between places you need to join convoys, which can depart very early in the morning (as the case of the convoy to Abu Simbel from Aswan, which leaves at about 3:00am!)
My friend said that they don't let you, as a non-Egyptian, take a lot of the public transport and you are fairly limited in the journeying between towns.
Luxor is fascinating - Karnak and Luxor temples are worth a visit, I would advise joining a tour group, not necessarily booking a guide, but just sort of tag along with another group - remembering to tip the tour guide afterwards. Thats what we did and they point out fascinating things, which you wouldn't notice otherwise, which honestly, make the temples far more interesting.
Abu Simbel is awe-inspiring, honestly. Its definately worth a visit!
Kom Ombo is worth a trip, as is Edfu. IF you can, try to visit Esna, though you will almost certainly have problems. My mate made it and he said its definately worth a trip...I didn't make it.
If you have never been to the Middle East before, stock up on LOTS of small change - lots of one Egyptian Pound notes. They will expect tips for EVERYTHING, seriously, pushing your cases at the airport...there are also hundreds of men wandering around the temples showing you things, and will expect tips, but a lot of the time its worth it. Plus, they aren't very good photographers in my experience, so if they offer to take a photo of you, make sure they do it properly!
I'd also like to visit the Western Desert - Siwa Oasis, I've heard, is fascinatingly weird.
This is probably too late, but oh well.