Let's see...
1. Six Degrees Of Inner Turbulence - An epic ride, and one that I take a half dozen times a year. As someone stated earlier, DT in a nutshell. Great from start to finish. (This is Dream Theater's 'Supper's Ready'.)
2. Octavarium - It's like a great meal, but with FOUR salad courses. The salad is good, but it takes a while to get through it all before the entree, which is killer! One of the best finishes to any epic. When the French horn comes in, it's just beautiful!
3. A Change Of Season - The LSFNY version specifically. The studio version is just OK, but live, its next level stuff. (I heard the live version first, which is probably why I'm partial to it.)
4. Illumination Theory - Unlike most, I like the classical interlude. It could have been blended a little better with the surrounding sections, but its a great piece of music. Like SDOIT, its sees regular play.
5. The Count of Tuscany - I just like this tune. The guitar intro, the rocking section, the 'Close To The Edge' section, the closing, all of it! It's all good, and makes a great epic.
6. In The Presence Of Enemies - I like this tune overall. The first 8-9 minutes is great as a stand alone. (Maybe it should have been.) Part 2 has many great moments, especially when the 'Patrick Moraz' part kicks in at the 13:12 mark. The very end is a bit anti-climatic for an epic. It sounds a bit tacked on.
Any good epic requires a big finish, needs to make those neck hairs stand up, and get those goose bumps going. The truly great ones can bring on the tears. Most of these check all of those boxes, at least for me.
DanLore