The Crusader admittedly is a bit hard to make out, but since these are [possibly] going to be game sprites, they don't need shading. Since light sources would change, it would be odd if every unit had changing shadows too.
Well, shading usually does help sprites in defining depth in their shapes, and most games, regardless of light source, do have shaded units.
Your point with the inability to recognise them probably comes from the fact that they aren't moving, I've made some prototype executables [with other units I've drawn, not these] but I don't think SEN trusts me enough to download a .exe [I don't blame you!]
Well, if they're animated, couldn't you use a .gif? xP But ya, that would help a lot. I for some reason rarely see
sprites of that sort animated, oddly enough, so it's what I'd come to expect.
Although, your issue with the Phalanx, if you previously didn't recognise it was a walker, how did "Phalanx" hlp you to identify it?
Its name in particular didn't help much, but context, given by the others' names, did.
I'm also fairly certain that the Aegis tank would be recognised as a tank fairly quickly by anyone who knows what a tank looks like.
Well, the turret looks rather awkwardly large, the treads take up more space on the lower area than they look like they have available at top, and combined with the fact that the first impression I got when I saw the front was of an airplane...
Moving, I'd probably recognize it, sure. I'm rather used to thinking in terms of games where that stuff's mostly background detail and 1x-zoom pixel art.
None.