I think one of the most common problems with turn-based combat in rpgs is that it's too slow. This is easy to fix: lower hit points (for the player as well as the monsters), raise damage, and raise the chance of a successful attack. Oh, and if you have healing of any kind within combat, scrap it. In an equally matched fight, you want characters to be able to absorb one attack without dying (because else there's no point in even having hit points), maybe two, but probably not more than two.

Hi Pixelamped,

Try to think about how your enemies make your player PLAY the game.

1. I think the charging enemy is a great start; it forces the player to move or face the consequences. Maybe the player could attack this enemy, then move behind other enemies, causing the charger to damage the other enemies? You could make this technique difficult to pull off so the player is rewarded by practice and gets the feeling they ‘discovered’ a sneaky trick.
2. The poison is also a good idea. Does the poison just cause ‘poison damage’ instead of ‘physical damage’ like a knife would? You could give the player a way to counteract the poison. Maybe an antedote that can be purchaced/crafted/found? I am making a game that also has an enemy that uses poison as a weapon. While poisoned, the screen becomes blurry (like Doom) making combat more difficult until the effect wears off.
3. You could try to produce different variants of base enemies. Maybe change something like skin or armor color so they look a little different, but also change the attack a little. Maybe white enemies shoot arrows, green enemies shoot poison arrows, red enemies shoot flaming arrows that start a small fire where they land for a few seconds.
4. One thing I am putting in my game is an enemy that alerts other enemies of you position. If it sounds its alarm, you can either seek cover and fight, or run away.
5. Also think of how enemies are introduced in the game. Are they just standing around when the player enters the area? You could have them come out of buildings, burrow out of the ground, parachute / teleport in unexpectedly. This could all be randomized.

Good luck!

Got a few suggestions.
Depending on how you display your health, You could lie to the player, especially if you show numbers or a simple health bar. Experiment with it a little until it feels right.

Let's say your player character has 10 HP.
I would multiply it by a factor of 10 for the display, so the player sees 100 HP. but as far as the code is concerned, it's still 10.
If the play takes 1 damage now, the player's HP should be 90 HP, then 80, 70, and so forth until 0 HP. In this case, the player may notice it's still a base 10 HP.
To avoid this, you may display the HP at an offset value of +/- some.

Some games will mess with it even more. Especially action games. Although I can't remember the game in question (might be Destiny). It has a damage curve on the HP, so when it says you are at ¼ HP, the game reads it as 1/2 HP. This gives the player the feeling of “OMFG, that was close,” getting the adrenaline pumping because the player thinks they are in danger regardless.
For this, you may want to increase the health and damage of the code itself.

Now, as far as the enemies themselves are concerned, I agree with @scott8.
"Try to think about how your enemies make your player PLAY the game."
I would add to that Emergent gameplay elements.
This could be pitfalls, fire, water, and electricity. Adding an enemy that can interact with the terrain can go a long way. You could add one that only pushes the player to their death but does not harm them directly.
A creature that goes out of its way to shoot or to be on fire for more damage.
A beastly priest that stays in the back, protecting the other enemies.
These could be used to show the players different ways of playing the same game.

I'm pretty sure the game Undermine would serve as great inspiration.

Hell, go wild and out there. Set it in a city with traffic lights and citizens everywhere to serve as your rooms. ranging from crooks, police, healthcare, and their respective vehicles. And the most fearsome of all tourists, and you just spilled their ice cream.

A common technique is a variety of enemies with a variety of attacks.

Soldiers with longswords, soldiers with short swords and shields, soldiers with spears, archers, slings, grenades, assassins with knives, dogs with teeth and claws, horsemen, wizards casting spells, boss brutes with tremendous hand-to-hand strength.

In addition to the methods of attack, mix up their styles. Enemies on patrol, enemies on lookout, enemies milling about. Once detected, enemies that charge directly at you, enemies that team up, enemies that find cover and use ranged attacks.

As you specifically mentioned Zelda, the game has typically always had groups of enemies presenting a challenge, or a single formidable foe by itself. You might get a camp with 3 bokoblin archers on guard, 6 bokoblins with various weapons sitting around a fire, a few moblins with different weapons, or maybe a boss bokoblin leading the group. Other times you'll find a lone lynel with plenty of attacks including element-magic arrows, trampling, spears, light swords, heavy swords, and magical fireballs.

This is an area where composition really helps. You can have a small number of creature types, a small number of attack types, a small number of weapon types, but then when you multiply them together in combinations you get a large variety.

pixelamped said:

you want to make damage high, and health low, won't this make it difficult?

The important thing is that the player's damage is high and the enemies' health is low. Pounding on an enemy again and again and again until it finally croaks is no fun, and (unless the enemy is a huge) not very realistic either. An arrow or dagger through the heart will kill instantly. The challenge of a fight should be getting that one hit in without getting hit yourself, not slowly trading hits back and forth until one combatant runs out of health.

If enemies fall quickly, the game may become too easy. So then you need to decrease the player's health to the point where the game is challenging again, without making it too difficult.