I think the best analogy to use for Parasyte is that it's like an ancient philosopher waltzing around a market while in disguise. You first approach it, and get the feeling you're talking to a common peasant, but then out of nowhere it reveals that it has depth and a cataolgue of interesting characters and ideas. And then, to complete the analogy, the philospher then stabs you in the heart and laughs at your pain.
The whole "peasant look" thing comes from the basic outline of the plot. I mean, "Teenage boy that with lacking traits but a good heart gains powers that allow him to become part of a secret, and supernatural society" is such a basic template for shows in general, and anime in particular, that I'm pretty sure they give them out at comic-con by the truck load. But Parasyte takes this basic template, and instead of filling it in with fanservice and muscular men screaming at each other, applies some actually decent understanding of good narrative.
For one, Parasyte understands how to write a character arc, and not just for the main character. Although MC Shinichi's arc is by far the most dynamic and well written, pretty much every other character has their own arc, even if only as a complement to Shinichi's. And when I say character arc, I don't mean "Character becomes more confident in their own abilities" kind of arc but a "character is hardened by the cruel world, until they become a fundaementally different character" kind of arc.
Which leads me to the second thing Parasyte gets very right; it does not hold back on consequences. When characters mess up, or lose fights, people die, and the course of the plot changes. It's not quite on the level of things like Game of Thrones, where everyone is destined to die a horrible death, but that just means that when people do die, it feels that much heavier. So don't worry about everyone you care about getting murdered, but be prepared anyways.
Of course, this heavy approach to consequence wouldn't work unless Parasyte had a well defined rule system, but thankfully, as mentioned, Parasyte is a smart lad, so it does. What each character is and is not able to do is made known explicitly, and when those powers change, they're done over time, to avoid those "Haha, I use power no one has ever seen before, and no one will see again" moments that plague other similar shows. This means that when a character turns a fight around, it's because they figured out a new way to use the powers they already had, and the fights feel so much more impactful for it.
So take this as a lesson, screenwriters. If you want to write a powerful and memorable action-focused story, remember that the key is to write a good story. Parasyte did just that, and earns not only a strong reccomendation from me, but a spot in my favorites. (Also, having a soundtrack that slaps also helps, just saying).