There is only one small negative thing I can think of with your land unit icons: the model tags are quite inconsistent. In the official HoI2 icons the infantry models have 1918, 1936 etc, all others have I, II, III, IV etc. You seem to be using a bit of both, airborne and marines have 1939 etc, paras and garrison have I, II etc. I've always thought it quite silly to talk about 1943 marines, since they are not available in 1944, motorized cav 39 is available 1937 etc. Quite confusing, to say the least. If you use the real model years instead of the Roman numerals why not use the actual historical year directly on the icon?
Btw Paradox should actually be paying you for this
Do you have any plans for making icons for any other nations? You could have some sort of generic icons for most of the things that are similar (inf, mtn etc) and use more specific icons where this is appropriate (tanks mainly).
Also, do you have any plans on making better brigade icons? I think the standard ones are rather boring...