What makes a great game? how polished is the experience ... and this,
IMO comes from looking at details.
I'll give you two examples of what I think are great games. How drawn in, is the player to the content. Lets take a look at two very different games that have the same effects on people.
1. Uncharted 2 - This goes without saying, that it is a roller-coaster ride of a plot line combined with very simple game mechanics, all packaged in with seamless story telling. To me, its the pinnacle of adventure story telling in a game. Graphics are awesome, but honestly ... the game itself is so good you dont notice. I had to tell myself to stop and look around to appreciate how good it looked. Its just a giant adventure and I loved every minute of it.
2. Plants vs Zombies - The amount of cuteness in this game is almost enough to make Hitler a happy person. On top of this, the carrot on the stick has a good balance. They give you just enough carrot to want more. The challenges outside of the adventure story are very compelling to keep playing, as well some of the hidden features. But I had such a satisfying feeling when I beat the adventure mode.
Both games, I consider very good and both are very different. But both I can easily pickup and play and enjoy. Even after being 'done' with them.