Tried some using the gameboy palette too. I learnt a lot from this, I really do rely on the model too much instead of using textures.

Some of the metal edges look entirely too soft, especially the transitions between the metal plates. One of the plates has an indented line that goes right up to the edge then has a small membrane to connect it, it looks weird! Keep the indent all the way or stop it way sooner. There's also a weird super-soft looking corner!
The little hood above the sensor seems to not quite be connected, I suggest making it part of the larger piece it sits on rather than separately floating.
I really liked the look of the polygonization on the rivet heads, I think you should make more use of this! You have a lot of very soft edges.
Also this may be my love of cartoony style talking, but I think you should make the gun barrels fatter, and the support column too fatter too.