A little work with an exacto and a small drill would help a bunch. The gun barrel on it's right hand needs to be drilled out. I has an inconsistant diameter due to mold mismatch. Just drill it out and it will look much better. A bit of white on the sensors/lights (red circles) would help them a bunch. Look in the articles sections on gems. Overall, not a bad piece. Keep at it, it gets better.
be sure to do your pre-paint prep work, esp on large models, fill those gaps, and sand those mold lines and you'll have a much finer finished product. not the most interesting thing to do, but very important none the less.
So this is your first large mini and this is my first post lol, we're in the same boat :) I'd say not a bad effort for a first try. Nothing I can point out as a glaring error, only keep practising to improve the overall cleanliness of your work. Take it easy a bit with the inks or wash you're using the blue has quite a heavy stain which spoils attempts to highlight afterwards. Also if you paint weapons in boltgun metal or similar, brush a little mithril silver over them as a highlight.
Finally, spend some more time on the base, I can see that's a stock dreadnaught base, adequately painted, but you'd be amazed how a little debris, gravel or flock will improve the overall effect of the mini. Keep it up dude!