At the heart of Maurice Merleau-Ponty's philosophy in Phenomenology of Perception is ambiguity. This ambiguity is the philosophy's strength, rather than a weakness. Because the human being in the world is in the end not completely definable because she is never completely definite. We are situated beings in an ongoing project of co-existence with others within the field of the world. When we realize the unfolding nature of existence, and our implication within it, we no longer see ourselves as either simply "subjects" or "objects"; we are "situated, contingent* beings".
The implications of this are stunning. We are certainly free, but our situatedness implies a responsibility to act in coherent welfare with other human beings and the field of the world. We have a duty to enhance existence not only for ourselves but for all.
Merleau-Ponty's philosophy is both more optimistic than Sartre's and more enchanting. He continually remarks upon the wonder of perceiving the world, the magic of being within it, and the luminous quality of the things in the universe. While I'm glad I read Being and Nothingness first, I'm exceedingly joyful that I did not stop with that book, but pressed on to Phenomenology of Perception.† I'll be reckoning with Merleau-Ponty's philosophy for the rest of my life.
*The 'contingent' aspect of this philosophy strongly reminds me of the Buddhist principle of paticcasamuppāda, or dependent co-arising.
†I also highly recommend reading Monika M. Langer's book Merleau-Ponty's Phenomenology of Perception: A Guide and Commentary as well. While Phenomenology of Perception is far more accessible than Being and Nothingness, it is still a difficult book, and Langer's guide and commentary is very helpful in clarifying it.