I love the concept. You've done a good job in bringing a mystical quality to the piece, with the dark background and soft glow. I love the stars dancing around the planet. The details of the planet are very difficult to make out, however. If I hadn't known the title, I would not have known that it was the world in the hand. More contrast between the land and sea would be good, and it wouldn't hurt if the sea were a bit bluer. Also, the hand would be more instantly recognizable as a hand if the whole thumb were included in the picture and the hand were tilted up slightly. Nonetheless, this is a good piece. The world sits very naturally in the palm of the hand, and is seamlessly blended in, and the vision is compelling.
The combination of the blur in the far tips of the fingers, the blue particles emitting from the planet and the intense details of the wrinkles in the palm of the hand really adds a flare of realism and fantasy to this piece. Nice work!