Luck in turn based games make some playstyles impossible. Being aggressive is hard. You may only have to be extremely unlucky in one attack to get completely exposed the next turn. In Wesnoth is even worse because you have to grind your units to death.
I know that the game is that way on purpose but I feel that it makes it a niche game. For me, it has all the bad parts of a card game and a an RPG.