Final Fantasy is one of those grossly monumental series with a reputation that each successive release is more divisive than the last. However, one opinion that the majority of the fanbase shares is a seething hatred of Final Fantasy II.
It's not altogether unjustified: Final Fantasy II is a hostile game. Whereas its prequel was a relatively lighthearted fantasy romp à la Dragon Quest I and its myriad imitators, Final Fantasy II is a tale of resistance against a ruthless empire. This theme of oppression extends to the game's mechanics, as well: after you enter the four main characters' names, you are not dropped onto the world map, but into an unwinnable battle against four black knights on horseback. Before you've even had a chance to understand how the game works, your agency is stripped away as you choose any battle option available and witness how none of them help you in the slightest. It's the 8-bit version of an action cutscene, as framed by the game's core engine. It is interactive helplessness — a narrative device exclusive to the medium of games — and this may just be one of its earliest examples. Later still, a town full of NPCs (usually the signifier of an oasis of safe interaction) attack you on sight, and they're no pushovers either. The many doors of a lengthy dungeon may lead to treasure, or deposit you in the middle of a room in which every step is a combat encounter — with multiple steps to exit. Okay, that last one is just bad design, though the message is clear: Much like the Empire of Palamecia, Final Fantasy II is here to crush your hopes and grind you into the dirt.
The most commonly heard gripe about Final Fantasy II is with its progression system. Sakaguchi and Co. decided to go in a different direction here as well, and eschewed experience levels in favor of skill-based progression. In theory, it was a neat idea, and one that allowed you to push your characters into a role of your choice and watch them adapt: use a sword to increase your sword proficiency, take damage to increase HP, use spells frequently to become a craftier magus. In practice, it was something of a nightmare. Enemies in the starting area were either too weak to make a difference, or strong enough to invalidate your attacks and wipe your party. The best tactic for useful progression? Get into an encounter with a weak group of enemies, kill all of them save one, and then cross blades with your own party members and trade blows, healing when appropriate (if a character dies, you might as well write that battle off). Furthermore, time spent in a single battle is a contributing factor to stat gains, so you really need to drag out every single mind-numbing scenario of self-flagellation. Even at the end of all that, there's a degree of RNG to contend with, so your efforts are disconcertingly intangible.
For all its innovations, Final Fantasy II is an exercise in frustration. However, it was a valuable experiment, and one that went on to serve as the groundwork for a cult classic.
SaGa, a long-running series created by Final Fantasy II's system designer Akitoshi Kawazu, reused that title's core tenets. The earliest SaGa entries were largely similar to their inspiration, though tweaked just enough to be a more playable experience. However, Final Fantasy II's unusual progression system reached its true potential in the Super Famicom's Romancing SaGa trilogy. Each of these titles is a very Japanese take on the Western RPG, featuring an open world, myriad side quests, and some of the most complex (not to mention overwhelming) character customization seen during the 16-bit era. On top of the stat-based progression that SaGa adopted wholesale from Final Fantasy II, Romancing SaGa added Skill Sparks: any time a character uses a weapon they're proficient in, they have a chance to "Spark" a new technique — right in the middle of battle, so it can be used instantly. Each weapon type boasts over a dozen techniques, and those dedicated enough to pursue the highest level techniques (surprisingly, not too big an ask) become an unstoppable force by the time the final boss rolls around. It's incredibly satisfying. This style of progression continued into the 32-bit era with the divisive SaGa Frontier series, which added even more techniques as well as multi-character combos.
Nowadays, the "use a skill to increase it" system pioneered by Final Fantasy II and SaGa can be found in numerous RPGs, from The Elder Scrolls to the post-2009 Ys titles. It doesn't always work, but when implemented correctly, it's a satisfying way to tailor your characters that also ensures their early game skills won't become obsolete.
Final Fantasy II, thank you for your service.