Not too bad, you did very well with the water though perhaps it could have been better placed. The sky is the wrong colour for the water, or the water is the wrong colour for the sky, I think; the water is too intensely coloured for such a dull sky. Also, the sun shouldn't be green, somehow you need to keep the blue from seeping in. I think I see water splashing against the rock there, if it is then some should be splashed over the rock to give a depth guideline. The dead tree looks like it's floating, kind of, work on the orientation and lighting, and give it a stronger shadow to really stick it to the ground.
You've coloured the beach perfectly, I'm very impressed with the suggestions of waves. Basically, I would change the rock and the sky in this painting, and maybe add a boat or some rocks or fish in the water to improve the composition, or something on the horizon would also work well. Very well, come to think of it. Again, the water and the way it laps up on the beach are remarkably well done. It even looks like you can see the bottom through the shallower water, and I know from experience finding the correct colour for something like 'sand viewed through several feet of water' is no mean feet.
EDIT: Oh, and the sun (if it were bright) would seem a bit out of place in this, methinks. It gives the feel of a cloudy day.