Took a 5 (6?) day tour of Tibet with friends. Stretched from Lhasa and Holy Lake Namtso in the North to Mt. Everest in the South. Our tour organizer, Amy, was terrific. She laid out the details well in advance. We knew the agenda, which is how the tour was chosen by my friends. (They were kind enough to invite me, so I can comment only on some of the "up-front" stuff.) Amy arranged all my permit paperwork in advance, and arranged to buy the most affordable plane tickets from Beijing to Lhasa for me. (I live near Beijing now.) She was also very friendly and proactive. She checked in with us (and the tour guide) on a regular basis to make sure all was well. And was very responsive when we needed her help with something.
The tour itself was wonderful. I have dreamed of seeing Tibet since I was a child. It was a magical experience. It is really another world.
The tour provided a nice balance between seeing more modern, urban Tibet (Lhasa in the North and Shigatze in the center) and scenic rural areas. If you are not familiar with China, bear in mind that Tibet is part of the less-developed rural/agrarian Southwest. It has a very low population density, so "modern, urban" has a different meaning than it would in many other parts of China. It is safe and clean - not an issue - but don't expect it to be Beijing or Shanghai!
To get between the clusters of beautiful destinations, you have to accept that there's going to be a bus ride. Lhasa and Shigatze are a long day's bus ride apart. In certain places, the roads are currently not in good conditions, so you have to bump along. Unpleasant at times, but nothing to be done about it. (We also had a lot of rainy weather, which increased some people's anxiety level.)
I won't belabor the details of the individual destinations - you can read about all that online - save to say that they were thoughtfully chosen, and provided what seemed to be a great cross-section of Tibet and its culture.
Our guide, Bandan, a native of Shigatze, was exceptional. Knowledgeable, warm, outgoing, pleasant, and quick to address the minor glitches that always come up during travel. A wonderful, protective guide, and a delightful person. If you get a chance to request him, I highly recommend it.
A few cautionary notes: Altitude sickness can really be a problem for some people, but can be nothing to others. Road quality is highly variable. By Western standards, the hotels may not seem top-notch, but they're just fine for the Chinese, and most of us who have been living in China for while. There's a lot of variation in room quality at even high-end hotels. Don't like what you get? Go fuss and get another room. (This is *not* easy during tourist season.) Chinese driving habits are more...assertive than Westerners are used to. I've been here for 3 years, so I don't think about it, but it made a couple of my friends squirm. (The driver knew exactly what he was doing, so even when it looked scary, I was unconcerned.) Get used to squat toilets - sometimes pretty rudimentary ones. And no toilet paper or soap. Always carry packets of tissue you with you, and hand sanitizer. Oh - yak meat is its own unique thing. I love it. But I was in the minority in my tour group! ;)