Comment by Panoramix

Well, Mars is so much farther away and much more massive so you need a lot of fuel if you want to come back. This is much more difficult than the extra fuel needed for the moon landing due to lack of atmosphere. Speaking of which, Mars having an atmosphere means you need complex heat shields for the landing. Furthermore it's so far that unlike the case of the moon you can't make real time adjustments from earth, there's a delay of several minutes. Then again you have dust storms...