I completely and utterly adored Secret of Mana right from the beginning when I saw how brightly colored everything was. The Boy's outfit is bright blue with a hot pink bandana, cape, and belt! It is all so cheery-looking. (The three PCs all have canonical names, but the English version of the game gives you zero way of knowing what they are. So the Boy got named after the BF, the Girl got named after me, and we named the Sprite child Coke because who can resist a lame pun. It is most certainly not me.) The backgrounds, the character sprites, and the enemy sprites are all just lots of fun visually.
There is a lot I loved about this game, but the biggest has to be that it works really well as a 2-player RPG. You can even do 3-player if you have the right equipment. It has a real-time battle system, no random encounters, and all the PCs walk across the map. So rather than having the Boy stand in for the entire party while in towns or traveling between locations and then just getting to control your character during battles, you get to control your character all the time (with just a few exceptions). You want to go talk to that townsperson? Go talk to them! You think it's a good time to visit the inn but your partner wants to visit the weapons shop next door? Now it's a race to see who gets to their door first. Or you can stun a monster then push it over to where your partner's fighting and then both of you can whale on the monsters at the same time.
Secret of Mana is super fun to play as a multiplayer game. Occasionally there's the problem of someone getting stuck because the party is too far apart but it happened much less than I would have thought and mostly to the computer-controlled third party member. Coke would get distracted trying to kill things and we'd have to backtrack half a screen to get him moving forward again.
The characters seem well-balanced to me, so no one's stuck playing the useless character. The Boy is the fighter, the Girl is the white mage and healer but also is decent at hitting things, and the Sprite is the black mage who is good at offensive magic but bad at hitting things. The BF says the game is a little broken in that the Sprite's magic is super-powerful when leveled, but the BF and I managed pretty well without using Coke's black magic ever. The BF ended up pretty leveled in all the weapons, I leveled the whip to maximum as well as getting very good at healing magic, and that strategy worked well and was more fun because we both contributed.
I really liked the magic system too. You learn new spells when you encounter an elemental creature that gives you their magic. So when you find Undine you learn water magic and you get fire magic from Salamando. Each set of spells has its own level (so I ended the game with very high Undine magic from curing everyone all the time but low everything else because I rarely used it), and the maximum level for all the elements depends on how far you are in the game. The weapons system is similar, but each weapon's maximum level depends on whether you have forged the weapon to that level. I liked the whip because I could hit things without having to get too close; the BF rotated weapons depending on the situation. (And because, as the Boy, his weapon skill for the individual weapons increased faster than mine did, he was pretty handy with all the weapons despite rotating.)
I could go on and on about various things I enjoyed while playing Secret of Mana because there are a lots of them, but but mostly it was the sense of fun pervading the game while still having a serious plot. The three PCs are all very expressive, the Sprite especially. The game does some unique things like letting you travel between continents via being shot out of a cannon and opening treasure chests by throwing them on the ground. The music is unique and fun and included a couple tracks that I just wanted to sit and listen to whenever they came on. The plot is fairly simple and not super unique but I found it engaging. (And, honestly, I find a lot of RPG plots pretty similar. Oh no, there are a lot more monsters than there used to be! Here, young boy, use this sword to go on a quest to find out why and save the world! But first, assemble a party of fellow adventurers and friends to help you with this task. And go fetch some special MacGuffins in order to advance the plot. Oh and don't forget to turn your boat into an airship at some point.)
So yeah, I found a lot to love in Secret of Mana. But mostly how awesomely it works with two people.