I can't stand part 3, but it's much more of a curio since Viggo Mortensen starred in it long before Lord of the Rings made him famous.
BTW, the original treatment of the movie had some really explicit sequences in it like a nude man being hung upside down and split in half with a chainsaw. I remember there was a Fangoria issue talking about the productions diaries of the director and he said how the producers were yanking whole sections of the script out as it was really disgusting in it's original form.
So it could've been even much more brutal.
You can spot Viggo in a lot of earlier movies.. He truly worked his way up. Leatherface, American Yakuza, and lots of small roles before breaking it big. I respect him for it, actually.
That said, while Leatherface is weak in some ways, I've always found it entertaining. I like the concept too - a badass survivalist against a family of cannibal killers. Ending is kind of blah (both of them) though.