I just returned from a visit to Kathmandu this April. I was hugely disappointed to see that Kathmandu was no longer the "lush tropical paradise amidst the Himalayas" that I had pictured it to be, but rather the worst example of uncontrolled urban sprawl and air pollution that I have ever seen. When I arrived in the valley after crossing through the hills we could practically cut the air with a knife! I asked one of my tour guides about air pollution controls and was told that these were in place, but that the police who were supposed to enforce the "green sticker" policy for vehicles in Kathmandu regularly accepted bribes in exchange for the green sticker on the windshield of vehicles permitted to drive in the city.
Nevertheless, I loved the people and spirituality that permeated every street and alleyway of Kathmandu. It is practically impossible to walk anywhere without stumbling over a stupa or some kind of shrine, no matter how small, and the people were some of the kindest and gentlest people I have met on my travels.
I will definitely visit Kathmandu and other parts of Nepal again in future and can only hope that some of the conditions will have improved by then.