Hi Chris! Welcome to the Cubebrush community 
You have an interesting painting going here. It feels like it could almost be environment art or a screenshot from a retro sci-fi game. (Which is not a bad thing if that's what you're going for.) However, I gather you're probably aiming for a more cinematic look, right?
If that's the case, there are two areas I noticed could use some adjustment. First, the level of detail: it's very consistent throughout the whole painting, which makes it more difficult for the viewer to concentrate on the focal point. Everything is calling for the same amount of attention instead of guiding the eye back to the man and the portal. You could try blurring out less important details toward the edges of the painting (Tilt-shift or Iris blur in Photoshop works great for that). Or, you could use lighting and values to draw out the main subject--which leads to my second critique point.
Values! If you were to desaturate the painting, all the grays would be very similar. Without contrasting values, the painting can tend to look flat. You do have the largest contrast at the portal, which is good--but you could easily take it further. Consider darkening up the surroundings so that the portal is definitely the main light source. The green light would be a great way to pick out the most important details while letting the rest fall into the shadows.
Anyway, that's my two cents. I hope that wasn't too confusing! Again, welcome to the forums, and good luck on your painting.
