Everything about this movie was brilliant when I first watched it back in the 80s - It also featured an iconic star in the form of Sylvester Stallone and two other fantastic actors in the form of Richard Crenna and Brian Dennehe.
The reason why this is the best of the Rambo movies is because of the pure thrilling stunts (motorbike chase, the fall from the clifftop, the jumping off trees and jumping on moving vehicles etc) the stunts are much better than those in its 3 sequels and of course the main reason for this movie being a classic is the performances of all the cast - there is real drama here when the local police are sent to hunt for a man that is like no other - they become the hunted themselves.
The movie is about survival - and the drama that ensues when one man wont give up to the face of his enemy - no matter what the odds - To me this is most watch-able because of the elements described.
This is a classic - forget the Bourne movies, forget Bond and Die Hard - First Blood is a real drama about survival of the fittest with a moving and dramatic performance from its hero.