@nForce, I have visited Lahore but not Islamabad. Lahore is a terrific place to visit especially if you want to savor the delights of the delicacies there, like the famous Lahori Kababs in Anarkali Bazar! But do ensure you pay for it as they refused to take any money from me saying that I was their honored guest from India!! Rather embarrassing!! But great and friendly guys out there. You'll feel at home!
Do take time to visit Shish Mahal (Palace of Mirrors) at the Lahore Fort, and Shalimar Gardens. And don't forget
Minar-e-Pakistan especially at night.
Cheers! Have a nice trip!