Decent Vectors and Colors, Poor Texturing

As stated above, I really like what you have here in terms of shapes and especially proportions, but everything looks so smudged and glossy it hurts almost just to look at it, compared with the elegant simplicity of old fashioned cartoons, or the realism of more modernistic 3D graphics.

Good geometry, but...

First off, your models are good. Each character and object are well-designed and look very distinct even in this group of characters. You also put a lot of modeling work in the background, which gives the image far more scope than if you had put a wall or an image. And the content of the image (a ragtag group made of robots, humans, and that rock-thing) is also an excellent choice.

However, this is what I like to call "good to first order", meaning it's excellent beginner work. To make it really look like something, ALL of your materials need to be deeper than they are. The jeans need very fine noise to reflect how actual denim has a lot of color variations; the blue texture on the ground isn't high enough resolution for the object you put it on, and I can see the bicubic interpolation; the texture on Rockman is excellent, but it also needs a normal map or "bump" map so that it looks like its made of separate rocks instead of a single rock with lines drawn on it; every material needs work in the specularity (how the light shines off of it, not how it reflects off of it); and many of your materials need additional layers of noise or color-mixing, and the steel especially could use some mirror-reflectivity.

Finally, there aren't enough polygons. You have a lot of smooth surfaces that are pretty clearly (to me) made of only a few polygons, so the smoothing is uneven across the surface (e.g. look at Silver Robot's body, with all of the uneven lighting and reflections as if it were made of clay instead of steel).

This looks to me like an excellent project for an animation course (i.e. given that you are still learning how to do it), but my comment is meant to tell you that even one more hour's work would substantially improve the model and image.