I really like the third-last one, there's definitely a nice sense of drama in the scene. The second one is also really nice, and I think you should continue working on it for sure.
To be 100% honest though, for the most part these do nothing for me. They seem uninspired and flat. They seem to build a lot on cliche's and fantasy elements, but for the most part are lacking any sort of dynamic range or depth. Based on the qualities of the 2 I liked, there's definitely potential to expand beyond that and make something unique.
In terms of technique, the colours you've used are great, so keep up the good work here. I'd invest in some differen (or more varied) brushes and sizes of brush. The brushstrokes here are all very one-dimensional, and there isn't really any weight dedicated to any particular area of the canvas. As a result nothing fully cathes the eye and your viewer is left to kinda just glaze over everything instead. This of course is with the exception of the two I already named, those are a step in the right direction.
The eye is drawn to large patches of lights and darks, and how they play against eachother to creat contrast. When everything is midrange in terms of tone, it gets muddled. The robot pulls the eyes' attention, and as a result we have a reason to move around the scene and take in what's going on.
One other thing to consider is style. These kind of seem unresolved in what they want to be. They're paintings, but also highly illustrative. You've got kind of an odd balance between those two. It would help your work a lot to go one way or the other. There's a delicate balance between realism and personal style, and these haven't fully gotten to a point where they seem well thought out yet on what they want to be.
I hope this doesn't all come off as harsh, it's all intended to help. :)