As our roguelike-project is starting to take the form of an actual, playable game (which I still won't publically reveal until we're at Beta-state), let me talk about the philosophy of encountering monsters in the game.
Monsters need to be scary. That is the very essence of the word. Monster. When I DM an pen & paper campaign, a fight that is not a threat to the player-characters' lives is not a fight worth rolling dice for. I dislike success-porn. When playing a video game, my opponents better be a threat to me too. If not, what's the point? For me as a player to feel good about myself? That's a bit like punching toddlers, isn't it? This is one of the main reasons I like difficult games for. Playing a game to overcome adversary (actual, effective adversary, not just pretend-one), not just to get a pad on the back.