Why would anyone want to play an RPG that doesn't let you control any aspect of your party's growth and development?
For the sake of comparison, let's take a quick trip back through Final Fantasy history. At the beginning of the original Final Fantasy, you must choose a party of four from a group of six different jobs (if you're curious, that's 126 different possible combinations). Final Fantasy III offers even more jobs to choose from (23 in the DS remake, which means nearly 15,000 combos!), and also allows you to switch jobs whenever you want. Final Fantasy II doesn't have jobs; instead, your characters develop their skills based on their actions in battle (e.g., the more they use a sword, the stronger they get). The point is, in all three games, you have options. You are in charge. And that's a good thing.
Now, let us return to Final Fantasy IV. You start the game in control of a Dark Knight named Cecil (possibly the lamest name for a Dark Knight ever, but you can always change it later) and a Dragoon named Kain. As you play through the game, new characters with their own specific jobs will join your party. At times some of these characters may leave, only to return later, often replaced by new characters in the meantime. Others will leave forever. And you will have absolutely no say in the matter.
For about 90% of the game, you will be told which characters to use. You will not be allowed to switch party members except when the game forces you to. Only after you've reached the final dungeon will you be allowed to change your party (which, as I understand, is a feature new to the GBA version; the original didn't even give you that much). And at that point, you will be able to choose a party of five from 10 different characters, except that you're always stuck with Cecil, so in the end there are a total of 126 possible combinations. So, for those of you keeping score, you don't get the same degree of freedom as in the original Final Fantasy until you're nearly done with the game. And by that point it's too little too late.
But it's not just building a party that you have no control over. The individual characters themselves are practically set in stone. Sure, you can give them stupid childish names like Buttface and buy new weapons and armor for them, but that's about it. You can't change their jobs like in Final Fantasy III (with one major exception, and that is a mandatory, permanent change). You can't decide which characters will learn which magic spells like in every previous Final Fantasy, because the mages will automatically learn specific spells as they reach specific levels. You can't even affect their stat growth in any meaningful way like in Final Fantasy II, since stat increases are predetermined until level 70 (and by the time you reach that, you'll be strong enough to do pretty much everything worth doing in the game).
Now you've got a party that you didn't put together yourself, filled with characters which you can't customize at all. So what do you do with them? Well, you send them off on a grand adventure, killing monsters for experience along the way. Final Fantasy IV introduces the ATB system to the series, wherein your characters must wait for a bar to fill up before taking any action, and monsters won't wait for you to move before they start attacking. The system feels a bit glitchy, at times skipping over a character's turn or letting another act twice in a row, but it's still playable. But playable does not necessarily mean fun; the high frequency of random encounters gets really tedious after a while, and you'll find yourself just mashing A to get through them as quickly as possible, or simply running away, rather than taking each battle seriously. Only the boss battles are relatively interesting. Granted, this is a common issue throughout much of the Final Fantasy series, but add on all the other faults the game has and you've got a serious problem.
Let us suppose that you've somehow managed to put up with this turd of a game long enough to play it all the way through. Well, once you've finished it, there's really no reason to ever want to subject yourself to the experience of playing through it again. Since you still won't be able to change your party or customize your characters, it's going to be exactly the same every time. The only part of the game that is potentially replayable is the final 10% or so, and that's only because you can actually switch characters at that point. But in the end, that is just substituting one group of fixed uncustomizable characters for another.
If there is one positive thing to say about Final Fantasy IV (and sadly, that seems to be the case) it must be about the music. Final Fantasy games are known for having great soundtracks, and this one is no exception. It's too bad that good music like this has to be associated with such an awful game. But on the bright side, after you've beaten the final boss, you'll unlock a music player that lets you listen to these gems without ever again having to touch the rest of the game. Or you can save yourself some time and money and just look them up on Youtube or something.
So to summarize, we have in Final Fantasy IV Advance an RPG that doesn't let you put together your own party or customize your own characters in any meaningful way, things which should be a part of any halfway decent attempt at an RPG. One of the few things you are given control over is the countless tedious random encounters, which are only made worse by the glitchy battle system. I can't in good conscience recommend this failure of a game to anyone.