My dream game would let you explore ruins of places long abandonned and forgotten.
My dream game would not insult your intelligence and would provide a light frame upon which it would let you build up your story from your experiences.
My dream game woud let you interact with its characters in multiple ways, while figuring a solution to the eternal problem of the "silent protagonist".
My dream game would surprise you by turning into something so much more than the action game you expected it to be all this time.
My dream game would end in a climax whose conclusion would be the one that made sense to you ; the one you were lead to choose through the dramatic progression of your actions.
My dream game would leave you free to not experience any of the above if you so chose.
My dream game was Dark Souls.