It almost looks too ‘perfect’.
I’d take a look at pictures of mountains and islands to see how actual terrain looks in real life. You will see there is a pretty wide variety of lumps, bumps, crevices, ridges and other features that will take time to model into your Terrain.
In truth with Terrian I usually just do really rough broad strokes with the tools at large values freehand until I like the basic shape of what I’ve done, then go back with the tools set to smaller values to make the surface more realistic.