I've thought about this question quite a bit, and found myself struggling to determine what I think makes a good landscape shot rather than a bad one. I think that landscapes are something that appeals to a gut reaction most of the time because of the feeling they evoke. It may be a feeling of calmness or trepidation, but it usually inspires a feeling. This makes it hard to determine what makes something good or not because it's so personal.
That being said, I think that one of the things that can make a landscape shot better is the illusion of depth within the photo. Something that makes the picture not so "flat". For example, green grass against a blue sky may be a nice image, but it's also "flat". In contrast, if a tree were added to the picture, it may create the illusion of more depth because you feel there is distance between you and the tree, and the tree and the horizon.
Not sure how much sense that makes though
