I think it's really cool that this game doesn't just give you an unlimited supply of any unit that you want.
It really forces you to make good decisions during battle to preserve your favorite unit stacks, and it keeps the overall game interesting by preventing you from sticking to only one kind of unit with only one kind of strategy.
Also from the responses this thread has got, it's clear that there are viable strategies for just about every unit; though one person might think one sort of unit bad, another person can say that they put it to very good use. So there are hardly any "trash" units, though I think it's becoming clear that some like the shaman might have slight "abuse" potential. Nevertheless, this game has MUCH better balance than other turn-based battle games, such as Gladius (which was still a good game!)
Good design, developers!