Looks good so far. Al the colors are in the right spot, and you've started on some good detail.
From the top, down:
I'd try your hand at edge-highlighting the green areas. It'll really make the model pop.
The holes you drilled for the multimelta are a tad small, and off-center. Perhaps make them larger. When drilling barrels, I find it really useful to scroe a small divot in the plastic/metal with my hobby knife to make sure the hole is drilled dead center. I don't always get it right, but it helps keep it closer to center.
Good work on the power cables between the sarcophagus and the body. They look nice.
Purity seal on the multimelta arm looks like a good start, though the wax needs some more color. It blends into the black of the arm a bit much as it is now.
Try putting a light wash on the gold on the sarcophagus. It'll add some contrast to the gold paint, and allow the rivets to stand out.
Lastly, finish up that base with some sand.
Good work, keep it up!