First, let us clear up some terminology. The procedure is often misleadingly referred to as a "head transplant." In reality, it is a body transplant. This is important. Whoever donates their body to Spiridinov will not suddenly wake up with his head on top of their body. Rather (if successful) Spiridinov wakes up with a different body where his used to be. What will the implications be? For most people, important but not earth-shattering. Most organ transplants, while rightly hailed as revolutionary in the scientific community, have little effect on healthy people (unlike, for example, computers), since most people are not into recreationally switching organs. Even those who have a heart or liver replaced will essentially be completely the same.
If Spiridinov has a successful operation, it will be no different, in that nearly all of his body parts have been replaced. It will be a fairly interesting situation, because he would need to adapt to having a body of a different size and shape, and in that sense it would be quite different from an internal organ transplant. His appetite might also change. But for everyone else, what possibilities does this open up? It may extend average lifespan, but not significantly. Most of the ailments that such a radical surgery could fix can also be fixed by much more specific, much less risky single-organ transplants. That said, the possibility of doing it all at once may extend some people's lifespans. However, the finite lifespan of the brain remains the limiting factor, as it so often is (think Alzheimer's). Put an 80-year-old brain in a 20-year-old body, and it won't live much longer than it otherwise would (one decade, most likely). Its main appeal will be to people like Spiridinov, as a final resort when other surgical methods have failed. But again, even if successful, the surgery will likely have so a low survival rate that most people would prefer not to risk it, even in the case of imminent death or paralysis. One application that someone will undoubtedly attempt would be a radical sex-change operation, though most people would think twice before doing this!
In answer to some the specific questions: there will definitely be protests. I doubt the CIA has any interest in quarantining Spiridinov, since the doctor who performed the transplant can do follow-up research as well as they. Not to mention that there are extremely limited applications, spycraft-wise. Having someone else's head is not terribly good for infiltration purposes. Although it is a long shot, the results of this surgery are well within scientific boundaries, and undoubtedly the surgeon will publicize any success in newspapers and medical journals, and make millions of dollars. As far as biological condition, I am a biophysicist by trade, not a physician. So I can add little to Black's comment, except to agree that rejection of the transplant is the main issue. If he survives, I might expect to see some motor control and balance issues, even if the body matches his own well. It probably is not realistic to expect that the "attachment of the wiring" will be flawless. He will be a chimaera, though, which should be fascinating.