People often don't think of Don Heck as being as unique, but there are occasions where Don Heck draws a character, usually one created by others, and he creates a look for the character so unique that it's really a shame that Heck's influence hasn't caught on.
An example would be Don Heck's portrayal of the Mad Thinker in AVENGERS #39. Kirby did the Thinker as the archetypal wild-haired scientist, aged and grotesque. Heck on the other hand, drew him as perfectly NORMAL...except for the eyes. You can tell by the eyes Heck gave the Thinker that that character was evil to the core. And further, Heck drew him in Rodin-style "thinker" position. Normal except for evil eyes, and the thinker position, are two characteristics for the most part not seen again with the Thinker.
Don Heck to my knowledge didn't get to draw the Incredible Hulk much, but in AVENGERS KING SIZE SPECIAL #1 (the very same story that features the Mandarin assembling the first Lethal Legion) you've got a Don Heck pin-up featuring the Hulk: unlike any other artist, he draws the Hulk as being explicitly Frankensteinian. Take away the green wrestler's body, you've got Boris Karloff's head, sans scars.
And then you've got Don Heck's Hercules. As much as I love and admire John Buscema, it's a shame his Hercules design was the more influential of the two: he drew Hercules as being a cross between a big crazy hobo and the God of Lumberjacks. He was hairy and with a gorilla body. Heck on the other hand, drew Hercules as a handsome man: he was Tony Stark with big muscles, more specifically like Steve Reeves.
The only thing that other artists took from Heck was how "busy" he made Hercules's outfit: he drew his shawl with scales, his belt buckle as a lion's head instead of an "H."