There is currently -no- interface for targeting unit enchantments. As far as I can tell, casting a buff on a stack simply applies the buff to a random target in the stack. So to apply an enchantment to a specific unit, this is the required process:
1) Select enchantment target
2) Unstack unit and move one space away
3) Select main stack
4) Select enchant caster
5) Select spell
6) Select enchantment target
7) Select enchantment target again
8) Move enchantment target back to main stack
Eight clicks is unacceptable for such a simple task in a modern interface, and it also wastes two completely unnecessary movement points. Instead, we should be able to choose a specific target inside a stack without the complicated stacking/restacking.
This is highly reminiscent of the aggravating buy/equip/trade interface. I've played text adventure and roleplaying games that require fewer key presses to interact with equipment and are more intuitive. There's no reason these screens should be separated. A single unified trade/equip/buy screen would be much better.
Almost forgot to add this...
Similarly, managing the enchantments is a process of complete guesswork. The "Enchants" tab on a hero lists what they have going, but not where the enchantment is. A hypothetical example: my sovereign applies 5 stoneskins, three to heros, one to a troop of hard hitting units that travels with him, and one from a long time ago to some now obsolete troops that have been delegated to gaurding wilderness improvements. I'm at my max number of enchants and I need to dispel one to apply stoneskin to my new son! But in the enchant tab, there's no way to tell which enchantment slot is affecting which unit, so I end up having to cancel one randomly and -hope- that it is the one affecting the right unit. If I choose wrong, I lose 10 turns of mana regen to recast stone skin.
This is not intuitive.
We should not have to leave a city for enchantments to be cast--this is another tedious and unnecessary procedure.
This causes bugs with certain enchantments being completely untargetable. Arcane Armor and Arcane Weapons both must be cast on the same square as the caster and are thus only applicable to random targets.