I thought 3 and 4 were just kinda there, being decent, but not improving on II. I thought BoF's performance on the PSX was mediocre compared to what it was on the SNES.
If you like the other BoF's as far as how they play, you'll hate the 5th. There is one dragon formation. One. It doesn't have armor, the weapons don't get much better, it penalizes wandering around, your inventory is nonexistant, you have to appraise every new piece of equipment you find if you want to use it, it's set in a cave, and it's what...12 hours long or so.
The game is hard though, which is why it's so good. In some places, you try to duke it out in human form because you want to protect your hero. But in others you get clobbered, and your only choice is to protect your party. And among the best things is that it's not even in blatantly obvious situations half the time. Sometimes you come across a normal fight, you haven't saved in a long time if at all, and you find yourself losing.
Go through a RPG without items, healing, and saving. Feel the sense of urgency that you *can't* afford to die. You can hit the invincibility button at any time and make it go away, but after the fight is over you have to live with the fact that you just burned 12% of your life. You'd best be sure you didn't have a choice. If you didn't do your best before you called the dragon, it's Game Over eventually.
The game simply does a superb job of balancing the fact that you are an invincible god and vulnerable group of mortals who are out of their league,at the same time. That's BoF.