I think a lot of qualities go into giving a song that epic feel, however they don't need to exist simultaneously. My examples would be:
Wintersun- Death and the Healing: What makes this song so epic for me is when they go immediately into a key change when they transition from the opening guitar riff to the vocals. Key changes are epic! And the fact that they do it with every verse and in each chorus just makes me wanna
Ensiferum- victory songs is great as well. This song progresses and builds with Ensiferum's characteristic folk instrumentals and heavy guitar, has a rockin chorus and a cool bridge part with a Capella Finnish chorus.
I could go on and on, but those two just came to my mind right away.