24 Episodes, Available on Hulu, Crunchyroll, (both subtitled), Adult Swim (dubbed, October 2015-April 2016 run)
"Someone on Earth has a sudden thought." Ok, that's nice, what is
...fine, yes, I am gonna watch this show, I want to find out what the hell is going on.
Izumi Shinichi is your typical slice-of-life anime protagonist, only it's established early that something very odd has happened to him, and soon we learn that an alien parasite attempted to take him over. Failing to reach his brain, it now lives in his right hand, and is called Migi (Japanese for "Right"). Because of the natures of the parasites, things get dangerous for Shinichi very quickly. Because of this, Migi and Shinichi are now closer to symbiotic (but never completely), creating a problem as they run into others who have been attacked and taken over by the aliens.
As the story progresses, we learn more about the parasitic aliens that come, such as the fact that...they don't know a lot about themselves, and many appear to only have the focus of reaching the host 'brain'. Also while they prefer and seem to all but demand hosts from humans, and cannibalize them in various ways, it doesn't matter what type of host it is...
THIS IS JUST THE FIRST EPISODE.
It is also important to add that the parasites themselves have a harder time fitting in in some ways. They have no memory or information from their former hosts' lives, having to relearn words, information, and not knowing basic human customs or reasoning. We learn early on that their first "directive" upon entering the brain is to "devour" the species, with the dog one conveying it's upset at having not reached a human and thus 'failed' it's directive. But beyond that, even as we learn a little more about the parasites, it's with them learning it as well, or through human authorities who are also learning about them. Neither side really have any information about the parasites, with even the parasites only knowing their original need and the 'directive', and often compare themselves to other animals who are 'born knowing' a trait without being taught (i.e being able to fly or weave webs...I call bullshit). They are, at their basic, a species created to 'rival' humans, but who have a more apathetic view of the world and who tend to justify their actions as "well, Humans are toxic" and that them not having similar emotions or views on emotions makes them more 'logical'. Also the whole "well, humans kill animals so they shouldn't be surprised when they're killed."
I don't always like that line of thought in a series, as it tends to feel like just a nihilistic view of humanity as something to be 'brought down' from it's lofty and undeserved place, or that apathy is a better way of doing this. The issue for me is that while the parasites consider themselves pragmatic and doing what they have to in order to 'survive', they actually aren't doing that. There are moments when they'll kill or talk about killing humans in a way that human never do with animals or other lives, resulting in a disconnect that makes them feel far less of a 'superior' group but more savage and apathetic. Migi tends to point out that it cares only for it's continued existence, to the point where it threatens Izumi and his family and friends with harm if it's found out. Yet when they meet someone who can sense them, Izumi is able to point out that even with telling them the 'truth', Migi only need pretend to be a right hand, or go to 'sleep', and they can easily avoid the issues. It takes HALF THE SERIES for Migi to actually think of this, and he doesn't actually think of this, he just acknowledges that Izumi is right.
Though to be fair, while the humans in this series have their flaws, mostly seeming to not believe or realize the dangers they're in until it's far too late (Kana's story arc made me groan each time she came on), they also gain advantages against the parasites often enough as the series progresses to make trouble for them. One manages to survive an attack, while another badly wounds another and escapes one after it reveals itself to her. Izumi himself, early in the series, manages to point out that he and Migi's main advantage against many of the parasites is that they are 'two' - while this is later changed by the introduction of Gotou ("Five" in Japanese) near the end of the series, it still remains for the most part. Even the parasites attempting to ensure 'safe' havens for their kind to feed backfires very early on, and for all that they complain about various human points, their own extinction occurs within a short period of time in the series, and they are unable to keep themselves hidden. Their contempt and misunderstanding of humans leads them into danger when facing Izumi or others in the series. Granted, some of the people in this series need to be smacked for the shit they pull, Izumi included, but the parasites themselves are often the ones who believe themselves in control and fail to realize when they actually aren't.
The music in the series is ok, but the main focus of any good anime is the opening and ending song. While the ending song, "It's the Right Time" by Daichi Muira, is a good slow song for a piano and to calm down from the action, the opening song of "Let Me Hear" by Fear and Loathing in Las Vegas is very much a hard rock cover, with the lyrics conveying the general theme of the show of humans and their feelings. While the lyrics and voice can sometimes grate, overall the opening is still fun and gets me ready for each episode, no matter what might have happened before.
While there are some differences in the English dub, the biggest one I can think of is the sound effect for the parasites. Most tend to have different sounds when they transform the parts they hold, especially if they 'open' up the skin or change it. Considering that most of the dubs today are very good, the voice acting matches a lot of the original and the way that the characters acted and reacted, but as it's harder to find online, if you can find it in DVD form or similar, I'd suggest that. Also because sometimes the extras are fun.
Parasyte ~the maxim~ is gore-filled sci-fi from the first scene, and paints a world where modern humans must deal with another species of near-equal intelligence that, when banding together and actually working to keep hidden, manage to remain outside of human detection and even gain some power. Some of the broad strokes about humans and the parasites in general makes it very much an 'us vs. them' scenario, it's in no way as insidious or scary as even the original Invasion of the Body Snatchers. A good watch for the alien design and the interactions between Migi and Izumi, especially how they change over time with the various trials and events the two go through, and work either with or against each other in their own ways.