You have a very good grasp on proportions. I'd say it's the most important thing to get right on a mech. Kudos to you for that. It's very difficult to fix later on without starting from scratch.
Based on what I can see, you also seem to (for the most part) make all the important joints look functional and with a wide enough range of motion. Range of motion is very important if you're ever interested in doing animation or just more extreme poses. A lot of people don't get that right. Old TRO art is very guilty of this for example. xp
Some ideas for future reference:
Based on how you detail your mechs, you either rely heavily on the old TRO art style for ideas, or you just go through the typical growth stages of a mech artist. (We were all guilty of it at some point. No shame in that.)
You should try and not greeble just for the sake of it and try to not limit your medium level detailing to just their underlying surface. What I mean by this is that breaking up your basic forms with medium scale detail work that flows over corners and edges is good. The less your underlying structure can be identified as a box, cylinder or sphere, the better. I hope I'm explaining this coherently.
Picture for aid:
You're almost about to make that transition. I can see it.
Personally I try to limit my detailing by following a few rules (and this is just my personal taste so take it or leave it):
1. Is the surface supposed to be heavily armored? If yes, then it probably should have very little detailing. I like to put most of my detail work somewhere "safe", ie not likely to get shot at. Big clean surfaces are not necessarily bad. A little bit here and there to keep it interesting is just perfection to me.
2. Does it have a purpose? The reason can sometimes just be "it looks good", but I try to come up with some kind of function to it. I often think about what's under the surface I'm modeling. Military things rarely have anything superfluous. Form and function go hand in hand.
3. How would this thing be put together? Thinking about how all the pieces come together from a manufacturing standpoint tells you where all the seams, hatches, ridges, bolts etc should be.
I think your Brigand is very close to what I'd make, following the above philosophy.
You've got talent for this.
Keep practicing! :thumbsup: