Otherwise known as Mystic Quest (in Europe). Worth a look for nostalgia's sake.
The game starts with you – the unnamed hero of this story – escaping from slavery as a gladiator and then immediately running into Dark Lord and his pal, just outside of the arena. Dark Lord pushes you over the edge of the waterfall but miraculously you survive, and so the (Mystic) quest begins. On the way, you become the protector of an unnamed girl who has mysterious powers and antecedents.
The plot is simple and mostly so is the game-play, though it has some nice variety to stop it just being "hit monster with sword until dead, now repeat until leveled up". You have a choice of weapons (and don't get rid of any, except your most basic sword) and they almost all have secondary uses e.g. your battle axe can also chop down trees to allow you to get to places you otherwise wouldn't be able to reach, and your whip can be used to swing you over gaps if there's something for it to "whip" onto (essential, since you can't jump). This brings me to the downside of the game-play – to change weapons, or do anything really, you have to keep using a long-winded menu system that really starts to grate after the first few minutes, but I guess in an early Game Boy game, now over 20 years old, this sort of thing needs to be forgiven. The puzzles are one of the greatest strengths of the game, some of which are pretty hard (you may occasionally need a walk-through even if you don't normally), which will keep you from being bored with the generic "hitting things with weapons/fire balls" part of game-play. As you level up, you get to decide whether you want to keep your hero evenly balanced between being both a strong physical fighter and magic-user or whether you want to push him much further in one direction.
The graphics are pretty much what you would expect for its age. If you ever played early Zelda games (the first one in particular) you'll have a good idea of the style. There is a map you can access to "help" but it's so basic (a big grid with the odd house to represent a town) that the help it gives is minimal. The Final Fantasy connection shows up in the sprites - you are pretty much the Warrior from the original FF, the dwarves are the same as FF II/IV and white mages and various others show up too.
The music, for its time, is really good but, of course, all the sound effects are 8-bit beeps and chirrups, so don't expect too much and you won't be disappointed.
One last thing to add is that a real boon of this game is that you can save anywhere, at any time, not often found in RPGs of the time but hugely helpful, especially in a hand-held game.
I can definitely recommend this game, especially if you love games such as Zelda, just be aware of its age and the restrictions this necessarily gives it.