Well first, I think you're overdoing it with the stalagmites/stalatites. Just a few here and there should be enough. They also take up too much space separately, and touch, which makes things seem very cluttered. I suggest you make them smaller all around. The shading could be worked upon, I don't suggest either of the ways you are currently doing it. Perhaps something sort-of in-between. I would shade them only slightly as a cone, but to defeat that whole gradient look, add some ridges and hard edges to make it seem natural and fitting.
If you're going with the hard-edge type thing for your tiles, then I recommend you just cut the shoreline off, make it go all the way down. Otherwise, make some transition tiles, a few curved corner pieces, and plenty of detail to make things transition naturally, and seamlessly. You'd need to do this all around as that's how you have it pretty much everywhere right now. It's a lot of work, but if you do it correctly it will be worth it.
Something about the perspective seems off to me, as well. Inside the cave, the floor looks kind of tilted, yet at the top the grass seems flat. At least that's how I've seen it up until now.