What are the best PC games with fantastical landscapes?

Skyrim has no concept of character classes, and there are no restrictions on what equipment or magic a given character can use or learn. A character's capabilities are defined by skills (e.g. heavy armor, marksman, enchantment) which automatically improve as they are used. Levels are gained by increasing skills, and each level grants one perk -- a passive, secondary effect which further enhances a particular skill -- and increases an attribute of your choice (Magicka, Stamina or Health).