Some people like the graphical engine, others - the system of character development or the battle system. Well, the truth is - all of these are the main ingredients of the formula named Best PC RPG!
Why the beautiful graphics are in charge?
I will try to answer. Many fans of role-playing games dream to escape from our world to another, where magic things can happen. They want to feel the freedom of this fantasy world with no need of making things, relevant to real life. If you are one of these people - then you definitely must place the graphical ingredient to your best PC RPG mixture.
Do you like character development? I mean when you gain experience, raise levels, and choose skills. For example, I am a very tiny girl (not strong at all), but I like to play a female barbarian with maximum strength and mighty blow. I have to admit that the beautiful fantasy realm is not enough for me. I want to feel myself as a strongest girl in the world. Some of us may say the brutal force is nothing, compare to the assassin's skills.
It depends only on what you seek.
Do you like the games like Baldur's Gate, Diablo or Neverwinter Nights - where the battle system is point to click, or you prefer games like Two Worlds - where you can take more action to perform special blows or attacks? And how about the combination of both styles - like The Witcher. It depends on what you want- more action or more strategy. I personally prefer the strategy battle types and I love the old Might and Magic series, where the battle is turn - based. If you like to play as a Mage or Wizard then the fight will be very different. Unfortunately, the spells and scrolls are not one of my favorite things to discuss.
So when you decide to play some new RPG game, first you must answer the question: "What exactly am I searching for"? Is it the beautiful fantasy world (graphics), or to feel stronger (character development), or just to fight someone (battle system). Even if you do not know the right answer, you will be much closer to the best PC RPG game for you.