Have to agree with MaximusPrime - these models are pretty damn good (love the lava though it could perhaps use a bit more extremes - some more black, and some more yellow/white).
To take your models on you could perhaps do with a bit more highlighting and shadowing - the guy on the right has much more delineation between his parts but you could try highlighting the tops and edges of his armour plates with some of the original red colour to make it pop a bit more.
You might also look into really going to town with some of the detailing, as that really brings a model to life. For example, the eye lenses look quite flat - try adding some darker green to the edges and front corners of the lens, with a small dot of white, or very light green to the upper rear of the lens, then coating with gloss varnish. This will give a much better illusion of the lens being an actual lens (you can find lots of tutorials around explaining how to do this with pictures, or even videos).
The only other thing you could possibly try would be to add some lighting from the lava (which is a bit harder to do as you have red armour and red/orange lava
), but you would get a kind of orangy glow to the parts of the armour facing the lava, particularly the feet and lower legs.
Otherwise your models are at a pretty good tabletop standard - I'd be more than happy to play against an army of your guys
