I'e had both knees done, both by nhs and both are as good as new. First one done 23 years ago still going strong.
I've had both done as well. One is fine. The other is a mess. Im 28 and can no longer play football, primarily because my knee never really recovered from the op I had.
Having said that, my waiting times for the operations I've had were both short, < 2 months, which for a non emergency op is really good. I was treated really well throughout as well, before and after the op, and indeed it's not that I wouldn't recommend the NHS generally, more that that single operation seems to have done my knee in.