Neither. It has cameos from a couple of characters and references to events from the comics, but it's mostly it's own thing with it's own set of characters and story.
I haven't played the third season, but the first was considered pretty great and probably did more to contribute to Telltale's success than any of their previous projects. The second season wasn't quite as good, but was still worth checking out. I didn't check out the third series in it's entirety.