An argument can be made that this is motivating people to use sunscreen, but a more widely accepted notion of motivational posters would likely classify this as some sort of public service or health awareness announcement. Judging from the large amount of 4's voted, I'm guessing a lot of people liked the image and voted down a bit for the message.
The shot itself is nice. Decent composition and lighting, if a little blown out on the woman's legs.
The font itself is a bit lack luster, and fails to deliver its message with impact. In these posters, how the message is presented is as important as both the image used and the message itself. It's a complete package and all three really need to be on the spot for the overall effect to work. Let's face it, these posters are pure propaganda and propaganda is an art unto itself.
This is a different twist to the usual motivational posters! This is great. Love your originality, not to mention your image is fantastic with super composition, and such lovely tones. Beautiful lines of the waves, too.