Just watched the first 12 episodes - first season - of this pretty disturbing series. Actually, I thought it'd be more disturbing than it was. After a little initial phase of surprise you get used to it, and those 'Parasyte's' don't look so vicious any more. Migi, in fact, looks kind of cuddly... until he (she? it?) actually lashes out with those vicious metallic claws and slices a head or two apart.
More so than disturbing, this series is depressing. People around the main character die, but even so that's not the most depressing part - it's how he's losing his senses, losing focus, losing his mind, losing himself, losing his heart? Cheesy, but there you have it. He still has altruity, that one thing humans have that makes them so strange, but he can't shed a tear even when those near to him die one after the other.
In conclusion, it's not a very uplifting anime! But, it is unique, it has the occasional flare of emotion and ferocity, it's well-animated and oftentimes unexpected in how the plot quickly shocks or shifts. You follow the character's evolution and struggle not so much against Migi but against himself (same thing?), how he distances himself from the world, from those he cares about, from the very human sentiments of care and sympathy... next season's bound to be interesting!
rated 4/5: fo shizzle