You get genuine Tibetan and Nepalese food here at authentic (read local) prices. Arrive early for a table by the window that overlooks Basantapur Square and watch the area transform as night falls. Sensational. It's also good in the morning for breakfast as the sun catches the square and all the traders set up, jockeying for position and polishing all their wares for maximum impact.
A young, friendly guy called Santa runs the Cosmopolitan, the staff are friendly and the service is attentive - most of the time. We never had a bad meal, but did speak to one traveller who did. Ask for kothe momos - they are half fried, half steamed, and the vegetarian meals and curries are also very good.
Our first meal here is a good guide to what you can expect to pay and the size of the serves. We were quite hungry and ordered a meal of steamed rice, vegetarian momos, chicken curry and large pots of tea and coffee.
The bill came to 200Rp - that was about US$3 at the time. We tried other (guidebook) recommended places but this one became our "local".
It's also worth noting that we saw a number of travelling families eating here as well as locals - testimony to the Cosmo's popularity and value.