I understood ndchristie's perspective breakdown just fine, and agree with the points made. Before his edit, i didn't realise the two dudes were supposed to be on the same plane (i thought the furthest one was actually lower, behind a dune, and the closest one on top of the same dune).
Although, assuming from the perspective indicated by the shape of the closest monster's body where it hits the water, it shows the horizon to be at the height helm showed (crossing the vertical half-point of the picture), where the observer would be above the scene, maybe standing on top of a hill. Contrary to helm's edit, i think the closeness indicated between the monster and the running folk shows a more immediate sense of dread, instead of not showing how much little ground is left between them by changing the perspective point (the original's composition reminds me more of a painting; helm's reminds me more of a movie).
Assuming the perspective stays the same: if these beasts are so massive, they're relatively close to the beach (or lakeshore?). The water there isn't too deep, so, they're not much larger underneath the water, which detracts from their potential huegeness. If you want to change this, change the shape of the monster/water intersection to show further distance, or change the shore to show something other than sand (maybe rocks, which could imply further depths to the waters near them).
Anyways, looking great, and great potential. I like the vertical format you used for your latest pieces canvas.