Why doesn't anything happen to Sam after the lightning hit him?

I was also expecting a worse outcome from lightning strike. But IMHO the harmless result is part of the movie's not-quite-realistic style. This cartoonish style is also evident when the junior scoutmaster rescues the senior scoutmaster by jumping an impossible distance. The movie is not meant to be taken 100% literally... it has a exaggerated-campfire-story vibe throughout.

A possible "dark" interpretation of that scene is that Sam died after getting hit by lightning and everything after that is just Sam's (or Suzy's) dream; that's why things got better from there.

When Sam is struck by lighting, there is a double meaning. First, it is in reference to the "electro-shock therapy" which is mentioned several times earlier in the film. Secondly, it is to open the ending up for interpretation for the wide range of the intended audience; for the younger viewers, Sam survives and lives happily ever after, and for the more intellectual viewer, cinematic devices suggest that Sam is killed by the lightning and the rest of the film following the lightning strike is an 'out of body' experience or 'near to death' experience. (Often associated with a triggered release of chemicals in the pineal gland.)

I thought the entire lightning strikes part was pointless drama.... the anticipation of lightning and storms, the ridiculously asinine sparks between the lips thing left me cold.