This is a rare one to be seen around, so you may want to watch it just because you might never see it again... but don't expect the same quality as other Jerry Lewis movies. Although there are some really funny scenes, Kreton is not half as funny as that other crazy alien, Mork (played by Robin Williams), and the movie lacks action and moves on very slowly through a thin plot a a lot of standard gags.
Review of Visit to a Small Planet
