Scheer,
How has this not happened yet? First Blood: great. Rambo III: just boring. But First Blood: Part 2? A masterpiece of bad. He blows up a helicopter with a bow and arrow! Even the title is an oxymoron. Why not Second Blood? This is in no way a continuation of the same story.
I like to think that at the end of First Blood, Rambo relapsed into a PTSD trance and all of the sequels are delusional fantasies.