I enjoy epic adventures as the capstone in the campaign.
When I say "epic", I mean:
(1) ...There's no tier of villains left after this one.
There is always a plausible tier of villains left after this one. In my game, presumably the capstone would be the Nameless Destroyer said to exist bound at the bottom of the negative energy well. This is a tier above the most powerful extant gods, so before the PC's could plausibly take on that, they'd have to have defeated directly not only the sort of deities like Gashuwen, Nuati or Karophet that back the dark cults that the PC's regularly face, but the chiefs of the evil deities like Barmal, Vargna, and Usurl, and ancient 'dead' gods like Old Chaos. The power level implied of the PC's is that of beings that have taken direct control of all of time and space. I would like to think that we hit 'Epic' well before we run out of villains.
(2) The player's characters are epic. The movers and shakers of the world treat the PCs as equals (or at least relative equals).
At various times, the PC's have had audiences with Benevolent Despot of Amalteen, the Painted Lady (head of a multination spanning thieves guild), and both the Hinga and Hurin of Talernga. The Hinga and Hurin are politically and militarily the most powerful individuals along the entire Storm Coast, and certainly within a 500 mile radius. Talernga as a city is among the 10 or so largest and most powerful on the planet, and one of the 5 or so greatest centers of learning on the planet.
It's worth noting however that none of these individuals were more than 8th level. Currently my PC's are doing more moving and shaking than most of the 20th level NPCs on the planet.
(3) The adventures are epic. Planar travel, time travel, LotR style armies, cities cleaved off the face of continents -- these are all appropriate in epic level adventures.
At first level, the party fled a tidal wave that washed away more than a 1/3rd of a city of 40,000 people and caused widespread devastation up and down a 50 mile stretch of coast line. They later learned that the tidal wave had been caused by a malfunction of an artifact of the legendary art mages from the age of wonders. After that, they participated in a massive night time battle between the city survivors and an invading army of deep ones. Then at 2nd level, they defeated an awakening centuries old draco-lich by destroying his phylactery. Since that time they've ventured into the depths of catacombs that had been sealed closed by the settings most legendary hero on the trail of a necromancer in search of a weapon that had been crafted to fight the gods and which threatened to destroy the continent or the world, and penetrated the secrets of the tomb of Menes III - in my setting the grandfather of Acerak the Eternal of Tomb of Horrors fame, fought a 900 year old curse manifestation related to the founding of the nation they lived in, participated in a massive naval battle between 11 warships mounting collectively hundreds of siege weapons, boarding and taking a ship in one case and helping to burn down another by dive bombing it on the back of hippogriffs, slew a dragon, and have been taken to the Astral Plane by a mysterious alley cat in order to learn about the power of the cosmic 'lightning' storms that flash between the positive and negative elemental planes.
All this before 7th level.
The consequences are epic. The result of these capstone adventures should shape the game world in a significant way. If you continue playing in the game world with a new set of characters, it should be obvious to all those new players how the previous group affected the world (for better or worse).
See above.
Mind you, I have never needed epic rules to play this type of game. In my long running 2e to 3.x campaign, the PCs finished at level 16. The final adventures were incredibly epic. The PCs went back in time to the creation of the universe, completely changed the time line and ended up blowing up their home planet so they could replace their existence with a version of history they liked better.
But I couldn't imagine using actual epic-level rules for those adventures. Building encounters became increasingly annoying after 11th or 12th level. The idea of having more than half the campaign take place over level 10 blows my mind.
My thoughts exactly.