Kathmandu is a tricky city. You will love it if you approach it with courage, energy, and an open mind. It is hectic and dirty and busy and occasional very hot and stinky. Many travelers spend two days shopping in Thamel and flee. To each their own, but I encourage you to really get to know this city. Be sure to visit places lik Pashupathinath, Swoyambhunath, Boddhanath, and be sure to take the time to walk around nearby neighborhoods. Allow yourself to feel overwhelmed and in awe.
Insider Tip:Don't get stuck in Thamel! There is so much to that city. One of the best things to do is walk to your destination! Thamel to Swoyambunath takes less than 45 minutes, and you see so much of the city you otherwise miss. If you're in Nepal you'll probably go trekking anyways, so it's best to warm those legs up.