Beach scene image on the left is without sky texture (the best one I had was CG sky's) so you need to add your own to the plane provided. Please let me know what you think.
Main problem with water imo is that it has that "lifted margin" and not wetting the sand like in the case of a beach, so it gives the impression that the water has really high density, like mercury.
First the sand, plants, and terrain mesh are OK, but I have some observations about your overall concept.
Try downloading 20-30 beach scenes from the Internet that match the concept you are trying to model and study how the plants, water, sky, and atmospheric look at different times of day.
Starting with the sky, I would say that your sky is too bright blue and sunny for the sun to be that low to the horizon. Either increase the azimuth of the sun or substitute a sky that represents late afternoon or early morning. And change the color and brightness of the sun to match.
The horizon is far to crisp and clean for a beach scene. The wind always kicks up spray from the water to create a mist as you look seaward. Additionally, there is almost always a natural haze to the horizon as well. You can create them with the Compositor (Andrew Price has a couple of tutorials on creating mist/fog with the compositor. Or use the Mist option in the World tab. But this can be tricky and you will need to expriement. Often times the mist will refuse to cooperate with start and end distances. In that case, I would create a clean mist on the horizon and then supplement it with a very large spot light using the "halo" option to fake volumetric atmospherics (see my Calm Before the Storm" scene on Blendswap for an example of using the mist and halo spot in combination. Also using a cloud texture with the MIst settings can add realism to the mist affect.
The ocean has many different colors to it. You should decide if you are creating a shallow lagoon with a bright aqua color or an ocean beach that will be darker and rougher. The water is too bright (specular)and isn't rough enough for an ocean beach, but the calm water is probably OK for a lagoon, but still the wrong color.
Notice how the ocean and lagoon often changes colors as water becomes more shallow. That is not an easy transtion to create in Blender, but you can see how I did it in my "Beach Scene" model on Blendswap. It takes a lot of experimenting and adjustments to get the blend right. And one formula does work for all beach scenarios. The color transition in a lagoon is more subtle but still there.
And you will notice that as waves wash upon a beach and reced the wet sand is much darker and smoother than the dry sand. Again, getting that color transition is the same technique as the ocean transition. You might fatten the gradient from the water line to the high tide mark and create that dark to light transition to sell the realism of the scene. Or move the camera back so that the beach gradient wouldn't be visible and not worry about it.
Sorry for the number and length of my comments, but you did ask for feed back. And I live on a beach, so I tend to notice the details.
Your plants are not right for a beach scene. Again, look at some reference pictures of beaches. Plants on beaches tend to grow in thick clumps (e.g., sea grasses, Sea Oats, palmetos, sea grapes, etc.) with small stalks of weeds thinly spaced radiating out from the clumps. Often there are breaks between the clumps that are bare sand or populated with a few smaller plants or ground cover specific to beaches.
Beach grasses don't normall grow out to the surf line and almost never grow out into the water as you might see on a lake.
Finally, beaches always seem to have odds and ends on them such as drifwood, clumps of sea weed that have washed up, garbage (unfortunately), and occasionally, but rarely, sea shells. I would suggest adding a subtle touch like that, but keep it subtle. You want it to add to the natural look of a beach and not dominate the scene.
In my opinion, the best photo realistic models are those where the subtlies "sell" the scene so that the eye is not drawn to any one particular item so much as it follows a natual flow or convergin force lines and the eye perceives the supporting details to be more realistic than they are. Artists often use the "S" curve to achieve that flow and support it with subtle force lines that help the eye achieve the intent of the artist. I'm certainly no expert at it, but it helps, I think, to at least be aware of the principles when organizing a scene. Check out some of the Photoshop tutorials on image organization. They will help even if you don't use an image editor.
I like your model because it makes me remind to bloxd io, my favorite design.
A few little changes might improve the realism of this scenario. To do this, add pizza tower to the outcome.
The concept and modelling are great. The implementation is great except for one flaw which appears to be in the Materials/Texturing of the water. The water, at least from the render on the right side that you posted looks a bit like mercury. I can't figure out what is wrong there but maybe making the water a bit more translucent might help?