Storytelling through high quality writing, large interactive world to explore, lore development, character building and development, interactive and engaging party companions, interesting and nonlinear main quest and plentiful side quests, branching dialog, meaningful and realistic consequences from choices, gameplay mechanics that only minimally depend on random chance or player motor skills.
These are the main things I consider to be what determines a good cRPG. The one thing that does NOT matter much for me is combat.
