This game lacks the excellent storytelling and interesting characters that make other Final Fantasy games great.
The first and most obvious comparison to FFV is the use of the job system. In this you equip different "crowns" to change jobs. The job and battle systems in this game can be quite entertaining at times, but certainly is not flawless. My major complaints include imbalanced job strength, inability to choose what target to attack and an uneven difficulty level. I found that certain jobs seemed overpowered while others were pretty useless. Once I found a combination of jobs that worked well for me (White Mage, Bard, Hero, and Black Mage FYI) I really didn't feel compelled to even try out some of the jobs you unlock later in the game. This ties into what I experienced as an uneven difficulty level since it was about the time I switched to using that job combo that the game went from very hard to rather easy. Also, while not completely related to combat, the game limits you to just 1 or 2 characters in your party for nearly the first half of the game, which severely limits your flexibility in what jobs to use. For a game with a title including "4 heroes" you spend an awfully long time as a small group of 1 or 2. Despite these complaints, I'd say the battle system is one of the best parts of this game.
Where this game really failed in my opinion, is in the story and to a lesser degree, with its characters. The story is very basic and predictable. It is mostly told through simple text dialogue usually with the leader of whatever town you are in or between the 4 main characters themselves. There's very little cinematic use of the camera or expression in the characters movements. Just because the DS has limited graphics capabilities doesn't mean you can't achieve high quality, interesting cutscenes/storytelling. On top of that, the game recycles its dungeons and cities, making you revisit all of them again about halfway through. Even the treasure chests you opened before remain opened, stripping you of any reason to reexplore these areas. The 4 main characters are likable enough, but at the same time nothing special. Some of the side characters were interesting too; in particular I liked the mouse Torte and the reluctant hero, Rolan. Unfortunately, I can't think of a single memorable enemy. They were almost all just "I'm evil, BWHAHA! Come find me chilling at the end of dungeon X." No glimpses of depth, just evil for the sake of being a bad guy.
The graphics and soundtrack both did their jobs but were unremarkable. I never found myself humming any of the tunes but at the same time I never found them annoying. There were some good looking environments and cool looking armor and weapon designs. There were also some very bland, nondescript areas, particularly some of the dungeons.
Wrapping up, by the end of this game I found myself wanting it to end and that's rare for me. I give this game a 3.5/10 with the idea that 5.0/10 is average. This game is worse than your average RPG, especially in the story department which is where an RPG should be strongest.