To be honest, animation isn't something that will look good without putting a hell of a lot of hard work into it. I just don't mean experience, I mean into one piece. This one piece of yours lacks much dedication in the animation. I'm not entirely sure if this is because of inexperience or lack of effort.
I see you nearly the whole walk animation is basically recycled from the rest of the piece. The legs, while appearing to move, are just the opposite legs flipped around. It's also been mentioned you need to up the frame count on the walking animation or you'll most likely never get anything close to smooth. There are a ton of topics covering walking animations, I can't pull up any right now, but you should be able to find something easily.
Mostly, your animations just lack movement. There's no reason the robot should be walking and only the legs move. Walking is a whole body thing... arms have to balance out the movement of the legs, the body will bob up and down as your legs bend(even in robots, especially since yours seems to follow human design). Again, a ton of topics on this.
It's true, while you may not have used a gradient tool, the piece is heavily filled with gradients... and this isn't just opinion. You need to define a lightsource and shade accordingly. If this seems confusing to you, I say grab the ol' pencil and paper and start on the basics by sketching some fruit or some other well-defined shapes.
Also, there's no reason to give up on this and try something better... just work on this.
