Simplified, but still offers something worthwhile.
Murky beginnings aside, I still have a deep fondness for this game, rooted in my childhood times with it. In my personal experience, the game served its purpose as helping acclimate myself to the splendid world of RPGs with a fun an easy to grasp theme. I was instantly drawn in to the classic look and feel of the game, coupled with the riveting musical score. The game throws you right into a battle, reminding the player that this is an old school RPG and turn-based combat will be your constant companion on this quest. Allies come and go and rarely stay long enough for you to care about them -save Phoebe-. The game features a world map that forces the player to follow a linear path; with a landscape riddled with towns, dungeons, and a unique concept: battlefields. These are obviously the game's attempt at holding players' hands and softening the blow of the grinding aspect (Often the most hated attribute of the genre) by offering rewards for winning a certain number of battles; neat.
The game's biggest challenges stems from solving the larger dungeons' complicated layouts, especially bringing to mind Pazuzu's Tower near the end of the game. This will give even seasoned veterans of the genre a prompt challenge, warranting a play-through. As noted earlier, the Mystic Quest features a musical score transcending far beyond the quality of the game itself. Atmospheric tunes and rock-driven battle themes are the order of the day. All of this culminates to an awesome theme for the final boss, resulting in one of the best RPG soundtracks you've never heard.
Spells are uniquely found scattered throughout dungeons and the environment, which upon acquiring allow you access to the spell for the duration of the game. There isn't a particularly large volume of them, however, with the lion's share of them being offensive blasters; few defensive spells here other than simple healing and cure. Weapons and armor upgrade automatically once they are discovered, and the ability to switch weapons mid-combat is a much-lauded decision adding some neat twists and turns to bouts. Random encounters are another hallmark of the Final Fantasy franchise not present here; monsters appear as sprites and the character can navigate around them when possible. However most dungeons will force you to fight more than walk around foes.
Mystic Quest may not be a "true" Final Fantasy installment, but it still offers plenty for an RPG aficionado to chew on. I recommend this game, don't believe the hype.