#9 Warhammer Online: Age of Reckoning
Warhammer Online: Age of Reckoning is set in the grimdark (yes, that's a word) Warhammer Fantasy setting, where war is perpetual and every race is at war with just about everyone else.
With the focus on player versus player combat, much of the game's action happens out in open world battlefields rather than instanced missions, where the goal is to kill the opposing army and take over their resources.
The game may be focused around player killing, but it also rewards explorers thanks to the inclusion of a Tome of Knowledge, a book that logs everything you accomplish, places you explore, and all the things you discover in your journeys.