There are some great moments here, no doubt about that. All the introductions are smooth, the caracterizations aren't overdone (for an example of that turn to Gilmore Girls). The place looks very real, the use of drugs and the diseases treated are well researched.
However I have to point out one or two mistakes:
-When Brian runs away the timeline is way off. Dr. Mike wakes up and finds Brian missing. Next scene: her riding on a horse stopped by the Cheyenne. Next scene: Scully awaiting Mike by a fire in the middle of the night telling her they will search for Brian together in the morning. But when they finally find Brian he looks as if he had just waited a couple of hours.
-The Characters that were recast later are too much alike too really remember them. In the next episode I had really trouble to sort them out again.
Plus as good an actress as Jane Seymour is (and I'm not saying she isn't) she really can't act crying. That part is way to melodramatic for my taste.
All in all a very convincing start to a great show.