There are many theories regarding the simplicity of a concept and how the success that concept receives in the marketplace is proportional its simplicity. Those theories battle each other like hungry dogs in a pound fighting over the remains of a largely unlucky cat. No theory gains more than a marginal victory over the others and must still fight with all its muster when the next cat comes along, but there are a few things we can say with relative solidity.
Take, say, a television show about a wacky scientist type who travels time in a time machine that is bigger inside than out with a variety of companions that he picks up and loses along the way, meeting all sorts strange, weird, and dangerous creatures in his journeys. This is a fairly simple concept, despite the protagonist's ability to traverse throughout time and space. It's this guy and these twink in this vehicle going to see all kinds of weird shit.
The advantage to a simple concept is that there is a low buy-in for a new viewer. You learn who the main character is, maybe three secondary characters and the plot for the day and off you go. This is also good for casual viewers, people who do not watch regularly, but do catch an episode here and there because they are brought up to speed within five minutes of the day's adventure.
Contrast this with a television series with no less than six characters who could be called a protagonist with a host of supporting and bit players in a large, interwoven tapestry of plots set in, say, Imperial Rome. In this case, if you don't watch from the beginning, you'll be lost, not know who'd doing what to who and why.
Thing is, though, simplicity does not always equal success. Simply put, there are more factors that contribute to success than a concept's simplicity. Otherwise, my idea for a sitcom that would be like "Friends" but in a leper colony would have been a hit.
