Golgo 13 is a retro-style anime that draws heavily from sniper stories about impossible shots in adverse conditions during the turmoil of the Cold War. If you don't know the manga by Takao Saito (the oldest still in publication, since 1968 and most likely about to conclude soon), the whole vibe of the series will feel wrong to some viewers, as Togo's narrative hasn't changed since the 70's. There is not need of character development, as the series depicts vignettes in the daily life of a professional actually doing his job, and nothing else. The characters around him are either service providers (weaponsmiths, intelligence brokers and prostitutes), clients or victims, and pretty much following the structure of the classic Japanese gangster movies, characters fade in and out, and never cross paths with him again. These 50 episodes are just like the stories depicted in the first 70 numbers of the manga. We don't know anything about Duke Togo (that isn't even his real name), and we never will (other than his code name is an "engrish" word for Golgotha and the number 13 a reference to Judas). He has an asian appearence, but never in the manga is stated as Japanese (he travels with a passport from an unspecified nation), as he speaks fluently russian, german, spanish, french, italian, english, mandarin, afrikaans and portuguese, all of them well enough to pass as a native speaker. I happen to find Golgo 13 quite refreshing, as the "assasination of the week" nature of the show is my kind of thrill (L&O style), and I don't have to worry about what's going on next, as do I know he'll get the job done and collect his 3 million dollars... or else. Suggestion: don't watch the dubbed version, and try to watch before "The Professional: Golgo 13" and the "Queen Bee" OVA, so you can get in to the mood.
I watched the first 8 episodes of the anime and was kinda disappointed... Not because of the content, but due to the strong episodic nature... Which is still an understatement. I checked out some of the later episodes and there is just NO development at all...
Golgo 13 doesn't change in his behaviour nor his skills. He seems to be a fixed point in time ;)
So you really have to enjoy it that way. Every episode is a case and the point of view is alternating between Golgo 13 himself, the victim, a policeman or some other person involved in it.
But without any character or story development the cases didn't have enough to keep me watching.