1) Lorca's theater is modernist. What does that mean? That he was searching for new forms of expression in the same way others were: Pirandello, Brecht... Both his experimental theater and his rural tragedies are modernist, though in different ways.
2) He is not expressing himself, his "self," but exploring multiple expressions of subjectivity, including ones that involve "blank" subjectivities.
3) His work can go in two directions: toward increased simplicity of motivation or toward ambiguity and complexity. For example, Yerma wants a baby but can't get one because she won't break social norms. E.g. having it with another man. It's not a complex psychology. Adela wants Pepe el Romano. At the other extreme are plays in which we don't know what the character wants.
4) Inseparability of his poetry and theater: see his theater as extension of his poetry in exploration of alternate subjectivities.
5) Lorca anticipates Beckett, but only if we liberate Beckett from the "absurdist" box and see his work in its complexity.
Let's put these ideas in a different order and make them connect:
1) Just as in this lyric poetry, Lorca as a dramatist is interested in exploring various forms of subjectivity.
2) The drama offers the advantage over the lyric in that dramatic subjectivity is the subjectivity of the character, not the implied author.
3) What he needs, then is modernist theater, since experimental techniques in the theater are aimed at exploring alternative subjectivities rather than "realistic" style character development.
4) Lorca's anti-realism goes in two directions: a simplification and stylization of dramatic motives, on the one hand, and their experimental complexity, on the other.
5) This leads us to Beckett, etc...