Ocarina of Time; The Well, Shadow Temple, Hyrule Market/Castle Grounds/Castle(AfterSevenYears)
Majoras Mask; The Moon, The Mask, The Transformation, Ikana Valley, the death of Mikau. And the bosses seem a lot darker. Same with the temples.
Serpent, if you haven't played Majora's Mask yet, you cant really state your opinion.
Anyway, No. Majora's Mask was much darker then Ocarina of Time. The transformation, the moon, Majora. Its one dark thing after another.