A classic from day one.
1) Plot. Golgo 13 is a spy/espionage thriller, akin to Tom Clancy or Albert R. Broccoli pic you may hanker for, and Vic Tokai uses scores of good spy movie cliches to set the tone. We've got a race to recover a hideous super-virus (biological-type, not computer-type -- don't forget, this was way before PC proliferation) called Cassandra G, you've got an omnipresent organization of evil headed by a boss whose identity is shrouded in secrecy, you've got various European and South American locales, you've got chapters that are titled after Bond novels, and you've got a red-hot hero who's an ace dresser / shooter / sideburns-wearer / ladies' man. And did I mention he's The Man With The Custom M-16? If I didn't rest assured any of the friends/enemies/info shills that you meet over the course of the game will remind you of that. Not that it's annoying.
2) Game conventions (cinematography, atmosphere, etc.). This thing plays out just like your favorite Bond movie. Remember when you hit the power button just to turn on your NES, and all of a sudden the bullet hole tears through the unassuming blue screen? How about the opening cinema screens -- the helicopter exploding in front of the Statue of Liberty? And that's before the gameplay even STARTS! I mean, was there a game that came before this that had cinema screens like that? Charming in their ambitious, 8-bit goodness.
And then there are those corny (and by that I mean "corny in hindsight, but at the time it blew your thirteen-year-old mind") dialog scenes, complete with the often-hilarious botched translations, varying in tone from suspicious to flirty to romantic to just plain weird (the midget boss character late in the game who lures you into the maddeningly-difficult gun battle in the rain forest). And who can forget the silhouetted "sex" scene, after which your energy is restored the next morning? Golden.
And did I mention you play as Duke Togo, AKA Golgo-13, The Man With The Custom M-16? This fact cannot be overlooked.
3) Gameplay. In a word? Multifaceted. This was a game of many gameplay firsts for its era. Whereas current "next-gen" games lock you into one dynamic for an entire game (e.g., platformer, FPS, RPG), Golgo 13 was one of the first (and of the few since) to give you every style possible -- and, in the framework of its place in history, to do it well. You start with your typical run-and-gun 2D side-scrolling action but, once that six-shooter gets drawn on you from the bottom-right corner of your screen, you're thrust face-first into one of the first (if not the first) FPS fight scenes on a home console. From there you move to (easily the first, and bloodiest) sniping scenes, followed by an arcade-ready flying-and-shooting segment akin to the old coin-op days of Defender or Stargate. Drop in a few mazes akin to Bard's Tale with machine guns, and you've got a enough gameplay styles to keep a man like The Man With The Custom M-16 satisfied.
4) Music. Often repetitive, but never boring. For only having a limited number of bytes to dedicate, Tokai did a fantastic job of developing music that supplemented the moods of the scene. And this has one of the best theme songs of any generation -- I don't see why this isn't a more prevalent ringtone.
5) Difficulty. This game was hard. Even with your Custom M-16, expect to get your arse kicked around, often using all of your 52 continues (get it -- it makes the game into a weekly, episodic serial. Incredible.) . The mazes are a jumbled nightmare, full of trap doors and sword-swinging enemies; FPS scenes often involve RPGs; you will swim between mines and deadly aquatic creatures; German streets will be filled with cold-blooded assassins who are ready to shoot you at a second's notice. Keep your life meter up, your gun drawn, and your eyes open.
This makes me want to plug the NES back in, grab my worn-and-torn instruction manual ('cuz it's got the maze maps), and spend another afternoon wishing I could wear a navy blue suit half as well as the Man With The Custom M-16. Timeless, classic, maddeningly difficult -- everything a great game should be in any generation.
6) And in one scene, he smokes a cig. You just have got to mention that somewhere, right?