No, he's not genetically enhanced.

He's been conditioned, which means he's been physically, emotionally and intellectually manipulated and trained until he's at peak condition, but also completely controllable through a combination of behavioural conditioning and a collection of drugs the Treadstone subjects take daily that make him susceptible to suggestion. He's been turned into the perfect soldier/hit man because he doesn't refuse orders, and just gets the job done, every time. It's worked so well that he doesn't even know his real name or real history. As part of his conditioning, he's been taught to handle pain, control stress, etc. so it can appear like he's superhuman, but he's ... not.

Which leads to your second question ... what's the most scary thing about making these hyper-trained, super controllable, near-automatons? When one of them breaks the conditioning, stops taking the drugs, and learns to think for himself again, realizing that he's been controlled and used as a walking weapon the entire time. Now that HE is choosing his targets, his controllers suspect who his next targets will be .... them!