Guild Wars 2.

Can basically level to 80 with only exploration, there are Low Intensity builds to have low difficulty playstyles that still are more than able to pull their weight.

Huge, water-colorish world.

Necro gets summons and Rangers get pets, where they have to find the juvenile versions of the pets in the open world to tame them and add them to their selection.

And it's free to play so free to try!