Monads are neither low- nor high-level. Monads are orthogonal to this. A monad (in the context of programming languages) is a generalised from of function composition. Instead of composing f : A --> B with g : B --> C yielding a function g;f : A --> C, monads compose functions f : A --> FB with g : B --> FC, yielding g;;f : A --> FC. Here F is come transformation on types. Monads connect the types FB and B in a canonical way. That's all.
