There is no doubt about it, UB is a poor place - but there are no McD's so maybe that's a good thing?
There really is very little to see or do in downtown UB, it's just a stopping off point for people on the trans-siberian train. Most of those will only stop one night, and hopefully spend it in the countryside outside UB.
However, not wishing to paint a very bleak picture - the Mongolian's I met up with, where very friendly and helpful, and there were lots of smiles as I wandered around UB.
One very curious thing I spotted was the Mongolian Mobile phone vendor - these people would sit on the street with an ordinary looking telephone, (the ones with a curly wire between the handset and box with the buttons on, but with the addition of a big aerial) and passers by would just ask to use the phone, and pay for it at the end of the call - a great idea! Why lug a mobile phone around, when you can just use one on the street corner..?