The idea of two non superpowered kids and their intelligent dog was questionable at best but trying to have the idea work over 45 minutes was a disaster. Even in episodes where the concept was interesting (a computer that eliminates all work and then promtly goes haywire, an alien stealing power, a scientist trying to change the Gulf Stream to heat his own country, another scientist trying to stop money being \'wasted\' on space travel, and an enviromentaist who is going too far) there are long dull periods which usially involved some improbable chase.
Adding to the problem was the fact that Marvin and Wendy came off as not all that bright and tended to get themselves into situations way over their heads. Then there was the question of why did the Superfriends keep these guys around. As lame as they were at least the later Zan and Jana had super powers but Marvin and Wendy had nothing.