However, as interesting (ahem) as this painting may be, I have decided to instead focus on a different one.
Observe my uncle. If his occulted guilt
Do not itself unkennel in one speech,
It is a damned ghost that we have seen,
And my imaginations are as foul
As Vulcan's stithy. Give him heedful note,
For I mine eyes will rivet to his face,
And, after, we will both our judgments join
In censure of his seeming"
Act III, Scene II, 85-92
This painting is especially interesting because it chooses to highlight the play-within-the play, letting the audience discover the true focus of the scene -- Horatio and Hamlet's careful spying. They two are hidden in this painting; King Claudius and Queen Gertrude on the left, and Ophelia, Hamlet, and Horatio in the shadows on the right. As one can see, all of the characters are facing forward and watching the play, except for Horatio and Hamlet, who are looking towards the king and queen.
Looking at the different expressions of the characters reveals their true feelings and intentions. King Claudius stares straight ahead without any emotion, perhaps trying too hard to hide his guilt and shame from killing his brother. On the other hand, Queen Gertrude seems much more affected by the scene than her husband (brother-in-law?). Her eyes are shifted to the left towards Claudius, and she's covering her face with her veil. Her physical movements mimic her inner emotions; she's truly ashamed of her quick marriage with Claudius after the death of her husband. I'm not sure if maybe I'm just over-analyzing, but it seems like the actor playing the king is also looking in Claudius's direction with an almost accusatory expression on his face... but maybe I'm just seeing things.
The colors and mood of the painting also reflect the book. The painting is covered with rich reds and dark shadows, creating an ominous feel that matches that of the scene. You can almost feel the ghost of old Hamlet watching over the crowd.