Another new member, great. Welcome on this forum. First post is not bad at all. There are a few things that I would change. You're right about the grass, give it some more color variation and more subdued. I would also lower the object from the pop a bit so, the leaves don't start above ground. If they get too short, just lengthen the stems.
I would make the rocky bottom of the island and lakebed more uniform. Keep the colors of the different stones more together, or apply an overall color set (on surface shader set to 50% coverage) after the stones, but restricted to the area of the stones).
And the snow in the distance; you could try a displacement intersection (in surface layer) to try and get a more distinct soft layer of snow on top. This looks like very dirt, old snow, but that might be your goal.
