They really missed the boat with epic spells. They should not be extensions of lesser magics, doing more damage or affecting larger areas. No, they should change the rules. Here are a few examples that are written generically so you can easily adapt them to your ruleset of choice:

Lungs Seek Relief alters how breathing works and all those within its area of effect must save or suffocate every round.

Free Internal Flames alters how much kinetic or electromagnetic energy is needed to start combustion- everything within its area of effect starts to burn if exposed to sunlight or moves at their full movement rate.

Sea Walking makes the surface of water as hard as adamantine. Air breathers needs to find their way to beyond the edge of the effect or break through somehow.

Speed the Flesh increases the reaction rate of living creatures to the point where a round for them is 1/10^th that for other creatures. But they also move so fast that they may run into things, such as walls and trees- Breath Weapon/Reflex/Dexterity saves should be used to avoid these impacts. Failure of the save should cause some damage.

Terrain Attunement subtly alters the land itself. The caster can select which ground is difficult terrain, up to the point where it is treated as a glass smooth cliff, and which terrain is easy.

Moon Chases the Sun changes how long the day is, but only in the area effected. Those who are in or enter the area affected age at the rate selected by the caster. In non-combat situations, this is usually used on a school or workshop so that students or workers can enter in the morning and leave in the evening several years older, their education or construction complete.

Sun Clouds Sight reverses how living creatures see- to them light is dark and dark is light. It also alters the range of sight to whatever the caster wishes.

Small World Writ Large alters how living creatures see- from the molecular to the galactic as the caster wishes. Non-epic creatures usually try to escape immediately as they have no understanding of what they perceive. Epic creatures that are trained may peer into worlds unknown to most. The spell also allows teleportation to and from, making this a sort of Gate spell, but one that can only be used by those who understand what they are seeing.

Cries Chill the Bone and many variants change energy types. Not only does Cries Chill the Bone turn sonic attacks into cold damage, it turns all sound into a decrease in temperature. Attempting to make any sound simply makes one chilly or possibly frost bitten, depending on how the caster uses the spell.

Turtle Beats Hare simply makes slow things fast and fast things slow. Mechanically this reverses the initiative order.

Stone Seeks Flesh makes creatures made of flesh, including corporeal undead, much easier to strike with stone weapons and implements. How much of a bonus is up to the caster, but should be a +20 at least to the attack roll. Damage is also increased, usually to triple.

Bathe in Darkness isn’t nearly as sinister as one might think. It allows all creatures within the area affected to not only ignore level draining spells and effects, but to heal from them. How much is dependant on the caster’s skill in casting this spell.

Something to keep in mind is that these spells can not be resisted as they alter reality, changing how the laws that govern the game function. The only way to ignore them is to use equally powerful abjuration epic magic.