This is awesome. I love the future-tech vibe, and yet a sense of a very old robot here in this picture.
For some reason, the sword, the girl with the short black hair and the scale of this makes me think of a Pacific Rim sequel. I know it looks more anime, and that was probably your intention, but it gives me such a cool mental image that I had to mention it anyways.
From the artistic side, I love the painterly quality since it shows the right amount of detail and realism without losing the sense that it's a painting.
I think this is absolutely gorgeous, I am not just talking about the colors and what we see in this picture, I mean this picture is not just a picture, it's a picture that tells a story. Anyone can interpret it in any way, some may imagine the character's journey to find this giant robot, or some may think even of how that Giant robot even came to be there and the long time it's been there and covered all in plants andtrees.
I think that it's very rare that an actual painting tells a story. Most just look beautiful and are just there.