Hi,
Im a physio, and spent years working with TKR patients, from pre-op to out-patient discharge.
Ive seen good ones and bad ones, but the underlying factor seems to be the motivation and outlook of the patient.
Those that are more positive and work hard, especially pre surgery, tend to do very well, those patients who give up easily or are more pessimistic seem to fare badly. I guess like anything in life!
If you are going for one, work hard at your exercises, get your quads as strong as poss, follow your physio's advice and work hard in hospital. It can take 6 months or so to get good flexion (bend), and extension, along with stability and proper walking pattern.
Good luck!