A few thoughts: As far as action stars go, few rank quite as high as Stallone. And of all his action roles, Rambo is his greatest character (no, I'm not counting Rocky). As the series progressed, the body count flew up higher and higher, but it's with this first movie that Rambo left the strongest impression, capturing the emotional side of a badass highly trained killer. This is one of the rare films of the '80s that succeeds both as an action movie and as an effective drama, giving Stallone more than enough material in both categories. The set pieces are stripped down (for the most part) and allow for creative battles, slowly escalating to all-out war. While I generally gravitate towards the ridiculous in regards to '80s action, the restraint found in this movie is both admirable and wholly successful in creating a realistic atmosphere out of something that might have otherwise been overblown action-porn. The cast is great, the writing is great, and the series this movie spawned was...well, never boring.
Who would I recommend it to? Fans of action need to consider this a high priority. One of the best of its decade and among the most influential of all time.