This series held surprises into the very last episode.
I'm not really going to include any major spoilers for the series in my review. The closest that I'll come will cover what you've probably heard about from any general discussion concerning the TV series, or the books that the story comes from, or the opening TV credits for the very first episode. That means that some key elements from the first 4 episodes, which covers the first 5% of the 74 episode series, will be mentioned. But it's hard to even say what the series is about without going that far, and you're likely to get more spoilers in any major review of the latest Hollywood mega-release anyways.
In life, there are two types of monsters. The first is the type that most of us have probably thought of in our childhood, the type that we feared under the bed or in the closet, the type who our parents or guardians told us didn't exist. The second type, however, is what the title of this series refers to. This is the type which adults do fear, the type that does exist. This monster can plan human deaths with the same nonchalance that others have when they decide the details of getting their next coffee.
Naoki Urasawa's story is one that covers such a monster, but this monster isn't the main character. Instead, the main character is the highly skilled Japanese neurosurgeon Kenzou Tenma, working in Germany shortly after its reunification. Tenma believes that all life is of equal high worth, and that the value of life isn't changed with wealth, fame, nor with celebrity status. But he discovers that the hospital itself doesn't share that belief. The life that he saved, the life which more desperately needed his skills, looked so much like another anonymous life that was about to get wiped out by the hospital's lack of ethics. But Tenma unknowingly gave life back to a monster. And for the first time ever, Tenma regrets the life that he saved; so much so that he finds himself forced to correct that mistake.
From this point, if you saw the opening credits which cover the first 90 seconds of the very first episode, you can guess the general direction of the series. Picture the TV series 'The Fugitive', but with a single storyline which went from the first episode to the last. Now throw in a detective (Inspector Runge) who is as calm, confident, and calculating as the devil himself, pursuing Tenma. There are also other characters in the series, who are crucial to how the story builds, and who are rather difficult to introduce clearly without spoiling some of the many subplots which build through the series. These characters include Tenma's ex-fiancée Eva, as well as a retired detective, a reclusive billionaire, two criminal psychiatrists, members of organized crime, ones involved in possible illegal dealings with the Czech police, a crusading defense attorney, and others.
There will be a few times where the main storyline seems to be put on hold, and a new storyline with new characters will be introduced. And you'd likely be wondering why things have taken a detour, or when they'll get back to the actual story. But the overall plot is much more complex and detailed than you may have seen on other serial thrillers such as 'Alias', '24', or 'Lost'. The seemingly disjointed story lines in 'Monster' slowly build to be a critical part in the overall plot, and the series overall doesn't have any wasted scenes or episodes (filler), nor the jumps and jolts which betray signs of last minute rewrites.
If you're hoping that the upcoming Hollywood movie based on the series will be as good, you might want to reconsider. For starters, it'll mean rewriting a story which takes 37 broadcast hours to tell, and re-conveying that over a time slot of 90 to 100 minutes. Also, it'll be coming from the same talent pool which took the highly rated Japanese movies 'Ringu', 'Ju-On', and 'Shall We Dance', and turned them into the mediocre Hollywood productions 'The Ring', 'The Grudge', and 'Shall We Dance'. (From 94-64-79 to 72-40-49, according to RottenTomatoes.com.) While Hollywood can make a good original movie occasionally, their record at remaking movies leaves a lot to be desired.
In short, this is one of the better suspense stories out there. The writing is solid, the characters are believable (even when their character changes), and the story always makes sense. In some story arcs, just when you think they're getting ready to wrap things up, they find a way to ratchet up the tension again. But it never seems forced, or cheap, like what is by far more common in most thrillers I've seen. 'Monster' is definitely a series which requires your full attention when watching it, due to the pace which events happen and the number of details which all come together as the story progresses. And if you don't mind a long story with a lot of twists and turns, this is definitely one worth following.