And the plot, the plot.
http://www.theanimereview.com/index.html?reviews/monster.html nails a lot of my own impressions, and once you grasp the full backstory and the reasons for Johan's choices (a very helpful guide is http://www.mania.com/aodvb/showthread.php?p=842678 ) as he learns more about himself and his lost memories, the intricacy becomes impressive indeed.
There are many characters, who weave in and out of the story unexpectedly, and by the middle I felt I had mental whiplash simply from how many 'good' characters turn out to be evil. No targets were spared in this noir hell, and I give it props for never pulling its punches, not even when aimed at children.
Johan has fantastic voice-acting and his plots and casual corruption of everything around him is fantastically written (the scene with the 'Red Hindenburg' and then him walking through the alley is a case in point), and scenes with him or his protege breaking someone's mind are almost at Hannibal levels of awesome.
At times I had issues with what felt like lazy writing, examples including Roberto (why won't he just die? how can he be a skilled hitman *and* a top criminal lawyer?!) and Dieter (go away already), and I hated Eva too much for any episode involving her to be a pleasure rather than a chore, but then episodes with Nina or Johan came along and I forgot my complaints.
The Munich library arc was fantastic, and then the Prague arc was also memorable, not just for finally giving some real answers. I see some reviewers say the Ruhenheim finale was satisfying but not as epic as they could have hoped for; I say that's balderdash.
My main regret is that not all of the side-stories matter to the main plot, episodes can move slowly, and now that I know the full plot, much of the mystery is gone; so I will probably never go back and rewatch _Monster_, though it is an excellent series. 74 episodes is simply too much.
(Incidentally, randomly reading on other topics, I think I've discovered the original for _Monster_'s General Wolf! It's http://en.wikipedia.org/wiki/Markus_Wolf : he was active 1950s-1980s, was a famous spymaster, left East Germany before the Wall fell, and guess what his nickname was? *"The man without a face"*! His biography doesn't fit the _Monster_ character perfectly, but the resemblances are clearly there.)
