Sorry for being in a rush, but
1) you should be consistent with your perspective. Check out some Commander Keen 4 (PC) screenshot for reference.
2) having all the sparkling of the water disappearing and reappearing simultaneously makes it look like the sun is blinking, not like they were due to movement of water.
3) altering the shadow according to the height of the platform is interesting, but you'd have a better result if the transition was smoother. You can achieve that with fast blink between dark-shadow and mid-shadow ... or you can alter the shadow's size rather than its opacity.
4) your rocks texture needs work. I'd suggest you give a look at
Indigo's stuff, and if that sounds too complicated for you atm, to opt for a more symbolic approach such as the one of
2DHero