Bravely Default overall is basically what if someone took Final Fantasy III-V, smashed all of them together, stirred the mix for a bit and made it a bit harder, as now you are playing it as an adult, and the served it up.
For me some of my first rpgs were Final Fantasy III and IV, and I love that style of gameplay. Bravely Default is perfect for me.
To say something about Bravely Default II specifically:
The game feels much more like a retro JRPG than BD 1 and BS.
The game is absolutely littered with treasure, which is hidden in interesting ways. Camera angles, hidden doors and switches and all. The last top down game where I walked straight into a wall because it was suspiciously placed, and got rewarded by a hidden path and treasure was an old FF for me, so this was delightfull.
They got Revo back for the soundtrack. This means no more cheap electro bullshit, but actual music. You can hear the comparison here:
This feeds nicely into the characters, as together with having banger tracks they are the most developed in the series. The little party convos are a step up in quality, and while no individual character reaches the quality of Ringabel they are the best cast of a Bravely game in total.
The combat is improved. They added conditional turn battles (the initiative system from FFX basically) to the Bravely formula. So instead of inputting all moves, and then it playing out depending on initiative like in Dragon Quest, you get a turn where you do something, and depending on how slow the action is you take your next turn comes up faster or slower.
The character development is also improved. You gain BP much faster, with a lot more jobs than before. This means you can mix and match jobs at your leisure and experiment much more. There is a story cap for your job levels at the halfway point of the game, so you can't get super late game abilities before that, but the BP gain is overall much smoother.
Hard difficulty is pretty neatly balanced. It cuts down on XP and BP you get. You still get BP faster on hard than in Bravely I, but you have to face bosses with much weaker skills, which means you need to either git gud or cheese. For me hard difficulty felt near perfect, a tad harder than Dragon Quest XI (on Draconian Stronger Monsters/no Xp from weaker enemies) which I consider the best balanced JRPG difficulty.
Some problems with the game I had were enemy design and cheesability. Some abilities are ridiculously overpowered, to the point where they butcher the otherwise nice difficulty curve. With how fast you gain XP and BP it is very easy to stumble upon a few of these early, and then just curbstomp the game to bits.
Also some boss designs feel just annoying, and made to be cheesed. There is a boss fairly early who is strange adds in combat. Those are immune to ridiculous amount of damage types. From my 4 dudes only one could actually damage the enemy, leading to a silly game of everyone using ethers on my red mage, who was the only one who could even deal damage. That should obviously never happen in a well balanced game.
Also it lacks some clear QoL and general polish, like missing a quest log.
If I were to rank them overall it is Bravely Default 1=2 > Bravely Second.