First of all, Burt Reynolds is one of the best action heroes ever. Forget your physical specimens of the 80s to present, Burty has the build of a normal dude, he gets tired, hung over, physically overtaken, but he's clever as hell. It's seeing him struggle through action sequences that makes them so exciting in this flick. Not to mention he's his smarmy self, and bit of a womanizer at that, but I mean, it was the 70s. Think of him as a bubbling Shaft, but less so than Elliott Gould's Marlowe in the Long Goodbye.
Added to all this you have an intriguing story, and some strange, yet amusing characters and situations. Not to forget a great and appropriate score from Jerry Goldsmith.
Almost needless to say: this one stands out.