Definitely Ultima VII, best in the franchise.
This... Why? Its like oblivion in 2D, but much better. :)
The gameworld of both games is renowned for its interactivity: virtually everything not nailed to the ground can be moved, taken, or interacted with in some fashion. It is possible, for instance, to bake bread, to forge weapons, to milk cows, to play musical instruments, and even to change a baby's swaddling. The Avatar and his companions will complain of hunger pains and severe thirst, and will even die if these matters are not attended to eventually. If they come across a disgusting or gruesome scene, they may groan and vomit; strong alcoholic beverages can also induce vomiting.
Both parts of Ultima VII allow free exploration of the game world, featuring a main plot and several other major subquests and tasks for the player to complete.