The problem I see with this is that people will end up giving up strategy in order to "protect" their leveled up units. Reading in some of the other posts, it seems to me that their are far too many bonuses that you can apply to a unit, this is going to cause confusion in the heat of battle and add to micromanagement. Hit points are still low as well, apparently, what is up with that? I can hear people screaming now, when a unit they have promoted with new abilities a dozen times loses to an inferior unit that wins without losing a single hit point - shades of civ 3.
I wish they had stuck with more hit points, and perhaps a half dozen "special" attrubutes you could apply to a unit ONLY when it wins a battle against a superior foe, say using enemy roads, extra move point, 1 extra tile vision, ignore move cost on hills, ignore move cost on jungle/forest, and retreat if losing against units with equal move points.
Well, we'll see how it all works out.