Many years ago I did a very long review of Tibet Cafe (the late, lamented spot near the Sheridan el stop) on Chowhound; you can find it
here. Among other things, I would simply note that (a) Tibetan food is not really that similar to Nepali given (among other things) the extraordinary differences in climate and and geography, and (b) the food is, for the most part, bland. If you've had excellent Tibetan food, odds are that it has been modified for American palates. Both Cumin and Taste of Himalayas describe themselves as presenting food from Nepal and India only; I saw nothing Tibetan on their menus (though, to be scrupulously fair, Cumin does offer momos, a Tibetan food "stolen" by the Nepalis and often presented as if it were Nepali. Any momos you're ever likely to have in a Nepali restaurant bear no resemblance to momos you would be served in Tibet...which is good thing.) As I noted in my Chowhound review, because of its blandness, some dishes are be served with a side of hot pepper sauce. In a word, you don't go to Tibet--or eat Tibetan food--to experience culinary delight.
Gypsy Boy
"I am not a glutton--I am an explorer of food." (Erma Bombeck)