This is coming out fantastic! I can easily see this being built in 3D. The only critique I could make would be to see more variation in uniformity in the size of shapes. Can't wait to see the how you will color this character!
Looking good, but some of the shapes need to be resolved and articulated with more clarity in terms of their 3D visual description, especially on the back view. I posted a paint-over where I inverted the colors because I think it's easier to see the shapes, and then tweaked a few things. The way the tank is attached didn't feel very secure and the harpoon looks like it would be hard to aim with one hand-hold that's so far below its center of gravity. Have you ever shot a long gun before? You want to be able to steady it against your shoulder and hold the barrel with your off-hand for better aim, so I sketched in some quick ideas for suggested modifications.
Also see if you can simplify the design a bit by keeping some larger shapes intact instead of subdividing everything. The variety of shapes between large masses or open spaces and carefully-designed detailed areas is what creates energy and interest, rather than simply a high number of details. Look at Jake Parker's designs for examples: http://mrjakeparker.com