The 4 elements feel and play exactly the same atm. I see 3 reasons for it:
- Enemies do not have resistances or weaknesses to specific elements.
Right now elemental damage is not negated by armor and only affected by elemental resistances. From my observations enemies with cloth armor (like the fire mages) have higher elemental resistance than armored enemies (like the knights).
When enemies and especially bosses are assigned with weaknesses and resistances the element selection becomes more meaningfull. - Elemental status effects hardly matter outside of boss fights, because the trigger condition is harsh.
Atm in order to apply a status effect an enemy must take ~45% of its total HP as pure elemental damage. This means only weapons with innate elemental damage like Spirit Edge, Moonshaft, several staffs or pure elemetal runes can cause a status effect in the first place. On regular enemies this hardly matters as they will die long before the condition is fullfilled.
The status effects are also unbalanced, electricity being the best one while heat/plague the worst, because their DoTs are just too weak. Personally I also thing having 2 DoTs is redundant, plague should do some debuff, like “enemies deal less damage” and not a copy of another DoT. - The most grave issue are the runes! All elements have access to the same rune attacks, which in return erases their identity.
There is Fireball, Ice Bolt & Plague Breath, which is just one rune recollored 3 times to match the elements. Then there are 4 [insert element here] Wave runes; or 4 [insert element here] Nova runes; or 4 [insert element here] Hellfire runes. The only exception is Chain Lightning, which replaces Fireball.
This issue extends further to elemental martial runes. There are [insert element here] Flurry runes; or [insert element here] Dash runes; or [insert element here] Throw runes etc.
My point here is, the elements must reflect a playstyle that you as a developer associate with an element. Then the runes must reflect those playstyles. Eg. you associate electricity with speed and mobility, which then translates into gapcloser runes like Lightning Assoullt/Lightnig Dash or into fast series attacks like Lightning Flurry. As a censequence other elments should not have access to similar attacks to not errode elmental identity; this means no more 4 [insert element here] Nova runes.