As I mention in my piece The Stages of the Swing, when evaluating a swing, I tend to do so using a number of Milestones.

• Release Point  
• Toe Touch
• Heel Plant
• Forward Movement of the Hands 
• Slot 
• Point Of Contact (POC)
• Whip Position
• Extension

The presence and sequencing of these milestones are very helpful in judging the quality of a swing.

Albert Pujols' Swing

Now, let me discuss what I look for with respect to each Milestone.