I hope that the reader finds this list informative, and as lengthy as it will be, it's by no means intended to show off. In the end it all boils down to opinion, anyhow.
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1. Fate/Zero & Fate/Stay night: Unlimited Blade Works - A highly underrated series that was adapted from a popular manga, Fate/Zero is the prequel to the original Stay night, which has three alternate routes, one being Unlimited Blade Works. The esteemed animation studio, Ufotable, took it upon themselves to adapt the series into a dark, mature story involving remarkable characters and gripping fight scenes. The synopsis: Seven Masters summon an equal amount of Servants of a different class to fight for them in order to win the Holy Grail and be granted a wish. Each character has a motivation for fighting and do whatever it takes to achieve their goal, although their sense of humanity is in question quite often. In terms of standing up to other great anime, I'd honestly say that both Fate series easily surpass all other contenders, including Fullmetal Alchemist [Brotherhood].
2. Guilty Crown - An original story that's pretty obviously inspired by Code Geass: Lelouch of the Rebellion. The story follows Shu Ouma, a tentative young man who attains the ability to draw objects out of a person's heart and is inducted into a "terrorist group" known as Funeral Parlor. He assists the group by hampering the plans of a corrupt government when they seek to execute or imprison the general populace due to suspicion of exposure to a virus outbreak. Sure, the plot might sound completely "original", but what sets Guilty Crown apart from most other tropes is the evolution of Shu's personality. He goes from an indecisive coward to a self-sacrificing leader who uses his power to protect his friends, and pulls through some otherwise impossible circumstances. This is the way that most protagonists should be handled, unlike the pretentious and tiresome mains who constantly scream their "dream" aloud (Naruto and Luffy, for example).
3. Attack on Titan - Whenever the small remnants of humanity are forced seek shelter behind towering walls, you know that there's something waiting on the other side. For around 100 years, the surviving numbers go about their lives with a doubt ever weighing on their minds., fearing that the rabid Titans would breach their "fortress" and exterminate them. Attack on Titan handles the extreme uncertainty of mankind and unpredictable nature of the Titans so well that it's hard to get turned off by any of the characters. Through their eyes, you see this monstrous force that is fixated on devouring each and every human being, and the monsters' origin isn't known to a single person. It's because of this constant desperation and anguish that almost everyone is relatable and should someone insignificant perish, you'd most likely feel a twinge of pity for them, too.
4. Macross Frontier - Almost the polar opposite of Attack on Titan, Frontier places the remnants of humanity in a floating space colony after Earth was destroyed by an alien force. The survivors supposedly escape detection until many years later--you guessed it--the aliens catch up to them and invade the colony, but with the usage of mech suits, they keep the invaders at bay. In particular, one of the main protagonists, the male lead, takes over the suit of a commander who had died and confronts the lead alien, driving it out. But outside of the well-choreographed fights, there are two other protags, female to be precise, who want to win ther heart of the male lead...by singing. Thing is, the songs are not the run of the mill J-Pop that one might expect; they are
catchy,
cheerful, and especially
epic. Guilty Crown also contains
vocal songs up to this standard, but they just can't match Frontier's musical quality. Combined with the auditory pleasures and the flashy animation, this series is both chilling and entrancing, especially towards the end.
5. Psycho-Pass - The not too-distant future is riddled with massive leaps in technology as the Sybil System is developed. The Sybil System is able to read the Hue, or the conscience in other words, by scanning a person's psychological state. If the person is caught by one of the scanners and gives off a high-rated Hue, then he will be subject to immediate arrest or sometimes disposal if he shows erratic behavior. Through this revolutionary enforcement method, humanity's very worth is questioned to the core, and eventually is manipulated by a man whose Hue turns up pure white. By his nefarious actions, the Enforcement Division--made up of an inspector and ex-criminals--are forced to take him down before he can throw the entire system into jeopardy. But is that the man's endgame, or could he be hiding a dark secret about Sybil System's very nature?
The second half of this list is pending...