I think that most modern hair transplants actually come out fine. I see a lot of results posted online and I can spot hair transplants in the real world very often (even if they came out great) and I am generally of the opinion that they helped the person who got them. I think it has a lot to do with expectations and discussions with the surgeon. If you understand what you are paying for and they do what they plan to do, I think most surgeries live up to expectations. When people go in under-educated (without knowing about the likely need for more than one hair transplant, shockloss in donor and recipient zones, protracted time to see a meaningful result, etc) or go to a bad doctor they tend to have a rough time and be unhappy.
Also, even the very best docs out there have some bad outcomes, so remember that no matter who you pick.