Final Fantasy Mystic Quest was created by SquareSoft(now Square-Enix) as an attempt to get Western gamers into the JRPG genre. For the most part, it failed in what it was designed to do and Final Fantasy Mystic Quest is today regarded as at best a kid's game and at worst an embarrassment.
My personal opinion of the game is to enjoy it for what it is: A Final Fantasy game for beginners, or Final Fantasy meets Zelda. Don't come into this game looking for another Final Fantasy IV or Final Fantasy VI, or even another Final Fantasy I, and then you won't be disappointed. If you look at Mystic Quest on its own, without comparing it to the epics that are FF2/4 or FF3/6, you can have a fun time playing and enjoying an interesting storyline in a unique world.
You begin the game at the Hill of Destiny as Benjamin (although you can change his name to whatever you wish.) Your village has disappeared, and you run into a mysterious old man who tells you to slay a Behemoth. After this is accomplished, you are told your goal is to save the world and restore the four crystals: Earth, Water, Fire, and Wind. This helpful old man will become your guide along the way, showing up in places to give you hints. Your first mission? Save the Crystal of Earth.
Mystic Quest is a beginner's RPG for certain, but the first curve of the game aptly epitomizes what is known on TVTROPES.ORG as 'early game Hell.' While are you saving the Crystal of Earth, you can die very easily in battlefields and in dungeon areas. Worse, you are either by yourself, or only have one person join your party, which is the mechanic for the whole game. Yep, you are either doing it alone or have one partner. Almost always, the partner will be much more overleveled than you are, and while you can gain levels, they cannot.
As the game progresses, you are introduced to several other characters. The first, Kaeli, joins you in Foresta, and gives you the Axe weapon. In this game, you retrieve weapons either when characters leave your party, or you can find them in chests. Unlike other FF games, there are no shops to buy treasure in, and you can't sell old armor and weapons- the game updates it for you automatically. On the plus side, you are upgraded to the more powerful armor. With weapons, you keep them all, and you can pick and choose for the main character (the other character will use what they join your party with.) and you get quite a variety of weapons here- bombs, a sword, an axe, and a claw. The claw is the most interesting, and its final form, the Dragon Claws, acts a lot like the Hookshot from Zelda. You can throw bombs too. See? Final Fantasy meets Zelda. Another unique feature of this game is you can jump.
The battlefield and overworld mechanics are where the flaw of this game comes in. On the plus side, you can see the enemies, so you aren't spammed by random encounters every 2 seconds. Also, the monsters change appearance as they weaken, which is handy. You can either put your 2nd character on autobattle or on manual, but the former has just as many disadvantages as advantages. Battles are mostly easy, but if your characters are paralyzed or petrified, and you only have 2 of them, it's an instant game over. However you can restart in the battle, so continuing is a slap on the wrist, if that. Some battles cannot be skipped, such as bosses. The only really hard ones that you might die at though are Flamerus Rex, at the start of the game, or the final boss, the Dark King.
The overworld mechanics are where this game really dropped the ball. I believe had it been a free-roaming overworld you could explore, this game would be infinitely more popular. Instead, you can only go in one of the directions the arrow points at. You can't freely explore the Overworld. Yep. That's about it.
Now, for the place this game really shines- THE MUSIC. Even those who hate this game admit the music is amazing, and they are right. From the title screen to the ending credits, there are no tunes I hate in this game. Amazing tracks include all battle themes, especially the regular battle theme, Fireburg, Focus Tower, Pazuzu's Tower, Bone Dungeon, Doom Castle, and Lava Dome/Volcano. I still have my CD of this game from back in the day when you bought them on eBay before YouTube, and I'm not ashamed to admit it sometimes plays when I'm driving.
A little bit about the characters: Benjamin talks a lot more than Cloud or Squall, and has a pretty engaging personality. His shrug when something unexplainable happens is cute, and will happen quite a lot. The female characters are incredibly strong women, especially for a beginner game. Kaeli joins your party and fights in spite of her poor health later, and Phoebe joins your party in a search for her grandpa and to save her town. Tristam is a bit of a jerk, always teasing Benjamin, but he is very helpful in the first dungeon. Reuben is my favorite of the male characters- you find him in Fireburg and he is pretty upbeat and mellow. All of them somewhat fit a stock RPG role- Benjamin is the knight, Kaeli is the white mage/healer, Tristam is the ninja/Thief, Reuben is a jack of all trades, and Phoebe is a red mage/archer.
Morally how does the game stand up? Well, there's magic. You learn magic from spell books too, as opposed to other Final Fantasy games where you just learn them naturally, or buy tomes, as in Final Fantasy II Japan, or from Materia or items or Espers. But this is really all there is to be concerned about. There's nothing sexual or overly violent in the game. No alcohol references, and the female characters wear appropriate clothing- they wear Greek like tunic-dresses that cover their torso and legs, and bare their arms, but only the most prudish of people would be angry at arms showing. I would feel comfortable letting even a very young child play it.
Overall, I like this game, but I understand why it is resented as a whole in the Final Fantasy fandom. It's a game you can enjoy for a day or so, but there's little replay value. Some fans have made fanmade versions to beef up the difficulty, but I have not played any of these. From a Christian perspective, I see little to be concerned about. From a secular perspective, it is what it is. It's a game for beginners. I found it to be a good filler between FF4 and FF6 back in the day. But I still agree that we should have gotten Final Fantasy V instead of having to wait for FF Anthology. A good used copy is a good use of money; no need to buy it new though.