Are sweet potato fries a healthy substitute for french fries? what's a good, healthy recipe for them?

Not really: The issue with fries is the fact that whether regular potato or sweet potato, they are generally prepared by deep frying which infuses a lot of fat into the fry. A better way to prepare them is to use raw potatoes so you know what you are starting with (prepackaged sometimes have salty and fatty additives). Then bake the fries instead of frying them. Good taste and healthier.