[Cosmic]

Vinyl,

This is based on viewing on my 58-inch Panasonic Plasma with a PS3 hooked via HDMI and Dolby Digital 5.1
"Deliverance" probably looks as good as it can, on Blu-Ray.
The film, being shot in a muddy brown/green palette, and with the color being 'pulled' in processing, will never jump off the screen.
That said, close-ups are sharp without being overwhelming, with good reproduction of the grain of the higher-speed film stocks used in some sequences.

The only 'problem footage' in the film is the B-roll stuff of the construction site and the explosion at the beginning of the film. It looks a bit flickery as if it's old stock or poorly processed. I imagine this was visible in the regular DVD as well. Other than that, the material is consistent.

Audio is typical of its period (sound of dubbed dialogue) and "Dueling Banjos" comes across well. Little fakery done; it plays as it is, cleanly and simply, in mono (despite the Dolby Digital encoding.)

As long as you don't expect it to look like the latest 'Batman', I think you will like it on Blu-Ray. They have gotten what they can out of that negative without resorting to nasty digital enhancements and similar, and for my money, that's the way it should be.
As mentioned, the commentaries are very good on here, and make for interesting background on the film.

It's something of a bargain too; on Amazon, under 'other sellers' you can get it for about $10 new plus shipping.

C.