One idea to make combat more strategic: potions aren't instantaneous. In Diablo II, drinking a potion slowly replenished your health/mana over a matter of seconds. In Dungeons & Dragons drinking a potion prevents you from attacking and defending. Personally, I like the second idea better. Drinking a potion requires you at least put your hand to your mouth for a second, causing you to lose any defense provided by your weapon (or a fraction of your dexterity.)
Some opponents could have disposable resources as well. Just when you think the mini-boss is about to die, health potion! An enemy wizard may have limited mana. To prevent players simply dodging attacks until their mana is drained, a wizard will remember which spells are effective. If you dodge three fireballs in a row, he won't bother trying that again unless you're in close quarters. If you continue to dodge them in close quarters, he'll save his mana for protection spells.
Limited types of damage. The twenty-odd damage types in Beyond Divinity were useless. Most were identical, just painted a different colour. Keep it down to 2 or 3 physical damage types and 3 to 5 additional types. Then you have a decent chance of being resistant to something. Why waste money or skill points deflecting a damage that you only encounter from 1 out of every 20 monsters? Also, have each additional damage type be unique in some way. Fire is wide, poison lasts, electricity is powerful, water can be critically damaging, wind knocks you back, earth is magically induced physical damage, etc.
With the thoughts jumping around on the combat system, whatever system is used needs to incorporate equally interesting physical and magical combat, while using the character's abilities rather than the players. My thoughts: click on a opponent to target them. Melee or ranged combat is automatic with the character attacking and deflecting and dodging blows. Special abilities and spells are a mouse-click or keyboard-key away. Larger monsters could have different sections to attack, possibly with a weakness.
With skills, try to balance the number of passive and active skills for each "class" of character. Often, fighters end up with a hoard of passive skills, requiring little interaction, and wizards with more active skills than they can ever hope to use. Different melee attack styles could be active skills. Have passive skills that suppliment a broad range of magic skills and let a wizard specialise. Also, skills that become obsolete are a waste. I'd rather see a fire bolt grow into a flaming inferno over 20 skill levels (some perhaps from augmenting passive skills) than have to dump the fire bolt in favour of a fire ball, then a flaming inferno. Any spell can potentially be the most powerful spell.
To prevent repeatative and sleepy combat, have opponents change their tactics from time to time. An orc may rush in with a powerful attack, may may resort to defensive or dirty fighting when things don't bode well to him.
Just some thoughts. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />