M. Emmet Walsh did not receive an Oscar nomination, although he did win an independent spirit award, for portraying Loren Visser.
M. Emmet Walsh portrays the private detective with a great deal of sleaze and sweat. Visser whole point in the film is to be an individualistic evil, who chooses to take the money to kill the couple, but double crosses the man instead killing the man and merely taking the money for himself. Visser only investment in the whole affair is his own well being financially, and physically, and decides to kill the couple after all only because he believes they threaten him. There is nothing technically emotional about Visser does even though it is all about himself.
Walsh is every effective in the role becuase of how casually he portrays the part of the detective. He wears his creepy smirk, and generally murky demeanor with gusto. He goes all the way with the sleaze and never strives from it for a moment. Walsh actually manages to use the sleaze to amplify the lack of morality within Visser. Walsh portrays no hesitation when Visser kills, he goes entirely unphased. Murdering for money is something that just comes as naturally to him as his generally slimy demeanor.
Visser comes in and out of the film as his evil presence, and Walsh becomes the chilling amoral evil in the film. Although he might not be as well together or as stoic as Javier Bardem in No Country For Old Men, Walsh is able to achieve the same effect with his performance. The effect is that the sinister force he creates when he is on screen carries off when he is not. The most horrifying moments in the film are when you are aware Visser is around, but you only hear him but do not see him. Like Bardem is so well able to the evil alive on screen that it even carries over when he is off.
M. Emmet Walsh despite portraying the most reprehensible character in the film, there is something strangely compelling about him becuase of Walsh's portrayal. He just wears the slime of his character with such as joy that he creates Visser into just a fascinating portrayal of a villain.The way he laughs in delight, even at his own end is played with menacing delight by Walsh. Every moment that M. Emmet Walsh is on screen he has a powerfully visceral effect with his performance.
I would say my only actual complaint of the character is that I wish there was more of Visser since even though he is the most mysterious character in the film Walsh still makes him the most interesting of them all. His somewhat limited screen time though does not reduce the great strengths of his performance in his demented startling turn as opportunist detective. After all it is really a compliment when the worst thing you can say about a performance is that you wish there was more of it.