A prequel is interesting depending on the setting and characters.
Star Wars prequels were supposed to make you see how Darth Vader came to be and how Palpatine rose to power, so they made sense.
Fear the Walkind Dead was *supposed* to show you how society crumbled into what you see near the end of Walking Dead's first episode (but it failed spectacularly).
In general, many people detest prequels because they tell events that have already transpired. Those people won't be interested in say, a WarCraft prequel telling how the orcs first appeared in Azeroth, because they already know the orcs are here *now* and the prequel won't change the story they already know (it will only enrich it).
For me, like I said above, it depends on what part of the story is told, and what characters it contains. If Shao Kahn was my favorite Mortal Kombat character and Boon announced an MK prequel which was about how Shao Kahn became the ruler of Outworld, I would be hype as fuck.