I've seen quite a bit of criticism about the lack of 'flavour' in Elemental, and I think one thing that contributes a lot to it is the lack of visual variety in your units. The problem is that if you want to put leather armour on your units, they will look almost the same as any other unit wearing leather armour, and there isn't the same visual variety as there was in for instance Galactic Civilizations II. This post is similar to another one I made in a thread about Elemental not having a 'one more turn' feeling to it.
I would like to see the visual appearance of units detached from their stats. The player should be able to choose how their units look and what stats they have separately. This would enable more interesting units to be created. E.g. barbarians who are tough like people wearing leather armour, but who are actually bare chested. Or you could have your army all wear plate mail but not actually have the armour stats of plate mail (e.g. because they have inferior quality armour). Basically, players can make the units they want and imagine whatever back story they want as well.
Failing this more choice in armour would be very nice. At the very least a good and evil type for each level of armour would provide some distinction between empire and kingdom soldiers, although that wouldn't really go far enough. But I think the best solution would just to be to let the players decide.
On a separate note, it would be nice to have some special powers you could assign to units which link in to special buildings (e.g. a holy aura granting damage bonuses against demons, but which means that a town will need a high temple to build that unit).
The unit builder has potential to be great (like so much in the game) but at the moment I find it lackluster and a little saddening. I don't have enough choice in building my units, and it isn't as fun as building ships in GalCiv2.