Holy COW! The size! The style! Love it! Instant classic for me.
Holy crap, lookit the size of that thing. 
A few spots look a little off when it comes to perspective (the big turret at the front stands out amongst these), but the overall piece looks great regardless. You chose an excellent color scheme for the vehicle, and you did a remarkable job with the dithering.
Pat yourself on the back for your hard work. 
This is the only drawing I've found so far labeled HD that actually IS HD *&* pixel art proper.
Anyone who happens upon this picture, in my opinion, this is what HD means. Take notes. A lot of notes! :)
This in particular, something about it strikes me as vaguely 90's beat em up arcade konami...like this could have been in TMNT arcade or something. Very cool, very large and very proper.