Y'all need two polls: one for theme and one for style.
Style:
GTA (linear missions in open world)
Just Cause (Missions barely there; world/emergent fun is the point)
Elder Scrolls (Freeform RPG in open world.)
Batman (World is chock full of stuff to do, lists to check off, etc. A big toybox.)
Minecraft (Creative/crafting/building game in open world)
DayZ (Survival in an open world)
Theme:
Modern (GTA, Saints Row, Sleeping Dogs, etc.)
Postmodern/Apocalyptic (Fallout, STALKER, arguably DayZ)
Future Earth (Cyberpunk? Maybe?)
Sci-fi (No really good examples yet, although arguably the X series is close)
Renaissance/premodern (Assassin's Creed, Red Dead Redemption)
Medieval (None yet, really)
Fantasy Medieval (Elder Scrolls.)
Prehistory/BC (Minecraft?)
On your poll: torn between Minecraft and Elder Scrolls.
On my "poll": Minecraft, Elder Scrolls, and Prehistory for theme.