Fortinbras along with Laertes offers up another parallel to Hamlet's situation. Fortinbras' father was killed by Hamlet's father. All three of these men have had fathers killed, but they all react to it differently.

Laertes is very hotheaded and is after revenge and is not above using trickery and villainy to get it (the poisoned sword).

Fortinbras is just as bent on revenge, but goes about it in a more open manner. He is crossing Denmark under false pretenses, but he and his army are there for all to see, they cannot sneak up upon anyone unless they are begin willfully blind (as I think Claudius was being).

Hamlet thinks and thinks and is slow to action but ultimately he gets the job done. ;-)