Some Spoilers...
OoT isn't nearly as "dark" as Majora's Mask mainly because people don't talk about death in OoT. Sure, Ganondorf destroyed the castle, etc, etc... But pretty much everyone you meet in Hyrule Castle Town as a child can be found later in Kakariko Village as an adult. Also, as a child, the general people don't know their world is about to change greatly.
In Majora's Mask, the majority of people *do* know what's going on and they really do think they're going to die. Heck, at least two people do die in the course of the game (Mikau and Darmani and very possibly the Deku Butler's Son *tear*). Everywhere you go as the days pass, everyone is talking about doom and gloom. Try this, if you haven't already... Open the path to Romani Ranch on the first day. Don't save Romani from the aliens and don't get involved with the Anju/Kafei storyline.
On the third day, visit the Ranch.