Sorry to point it out, but I feel this lacks originality at the moment. It looks like you specifically chose all the elements of a generic plaformer tileset: angled rocks used as borders of "cave", grass, pine trees background, summer light, white daisies...
The asymmetric lighting on the forested mountain is a breath of air however, and at least the main character does not look like a RPG archetype. But here's something you should consider when fleshing out a landscape : What makes your scenery / world different from every other nicely-pixeled platform game ? Can you give your own touch, your signature ? Are there details that you want players to notice, in order to make the player see this place as real, instead of a generic gaming background ? For example, carvings in stones and trees hint at a human occupation and culture. Animal tracks, burrows, nests, all hint at a population of wild animals.
The downside of giving more character to scenery elements is that the player may notice more the individual assets that you re-use in many places, but in my opinion, it's worth it, and you have the technique to pull it off.