Macs used to be the end-all for graphic and photo manipulation. That was when Adobe developed their products for Mac and then ported them to PC. They don't do that anymore. PCs used to be the end-all for video games because developers would develop for their saturated market and not bother with Macs due to the costs of porting the game over. Many of them don't do that anymore.
Say hello to 2013 oh you forum goers spouting misconceptions over a decade old.
As far as good games well ... the first challenge is to figure out a good MMO that meets your needs. Based on your description of choice and freedom your wants sound less MMO and more solo RPG like Fable or Skyrim. MMOs by design restrict your choices because the focus is playing with other people. So they want to push you in that direction.
Do you require your games to be fully Mac compatible, or are you willing to run the games in a virtualized windows like Parallels or Bootcamp? If so you're choices will be infinitely more expanded, but of course the games may not run as smoothly as you'd like (or they could run just fine). Skyrim is currently PC only but
some people have had great luck with a mac port
If exploration and absolute freedom are what you want though... I really think you should look outside the MMO genre because that sounds like you want a sandbox.