Someone said it before "Sacrifice". Good story, funny and awesome character, great lines, awesome gameplay. Truly epic spells. You cast tornado, you don't get some swirling wind that picks up some stuff for awhile, no the sky blackens, lightning flashes and a funnel comes crashing down to pick up a large group of anything friendly or enemies and hurls em skyward.
If you can manage to get your hands on it, Kingdom Under Fire: The Crusaders has epic gameplay. The voice acting is tolerable, and the translations suck. But they are some truly epic moments especially on the dark campaigns.
Game design though I'd have to go old school import Full Seiken Densetsu 3. I might have misspelled that but the story plays out differently depending on who you pick as characters and each character has a tiered system of advancement.
Now as far as story is concerned, in a single game its hard to beat KOTOR or Mass Effect but as a set Legacy of Kain is pretty damn epic.