I've been replaying Furi on Furier difficulty since I heard about the DLC which adds one two new bossfights.
Overall I did like it, each boss has their own personality in terms of character and fighting style and makes the most out of your limited moveset. I feel like a lot of people who call it too shallow went in with different expectations, expecting something along the likes of DMC or NGB, when the most apt comparison for Furi would be Alien Soldier by Treasure, which is another boss rush game featuring identical approaches to gameplay (speedkilling and not taking hits as a measure of score, high-level gameplay more centered around optimization than survival or stylish gameplay, parrying/playing defensively as a means of recovering ammo/health, lots of variation in terms of boss fights, and so on). If you think Furi is missing something, try playing Alien Soldier and see if AS needs more.
The dashing is rather inelegant. Unlike most games where you dash on the press of the button, in Furi you only dash on the release of the button, most likely a result from your dash being chargeable so you can instantly cross larger distances. For something you want to execute ASAP like dashing you want to do it fast, so it's hard to accomodate. So instead of dashing forwards through waves twice, you dash forwards, backwards, and then forwards again so you have enough space to execute it to begin with. There are a lot of times when I feel it should have just been an on-press command, but I understand why they did it. If you were able to constantly dash around, most of the wave attacks could be dodged with incredible ease while the melee attacks of bosses would have trouble connecting to you at all. This way you're asked to commit to your dashes, much like the fixed jumping arc in Castlevania games. It doesn't really feel right, but at least they built the game around it.
Most of the attacks are well telegraphed and the way the fighting goes back and forth is quite enjoyable. But if Furi were a simple case of call and response as most of these kind of games get unfairly ridiculed for, then it'd play out the same all the time. You can play aggressively as well and manage to sneak in a few extra hits to break the boss' combo or increase your best time. For example, there's a lot of techs involved in dealing more DPS. You can keep firing at a boss while parrying an attack string. When a boss is on the ground as you're about to enter the melee phase, you can instead begin a melee combo from a distance and hit him with the fourth and final strike of your combo which is a guaranteed knockdown, which gives you enough time to boost your attack. You can parry bullets for bonus damage and invulnerability through bullet waves, but you can't Royal Guard your way through entire bullet waves. On Furier the vulnerability window of bosses for melee attacks is much smaller, so a two-hit combo followed by a half-charged slash will deal the most combo than a three-hit combo while you're unlikely to land a 4-hit combo unless you were really fast. On top of that, there's a lot of boss-specific strategies as well.
But while this is one of the strengths Furi is striving for, it strangely also does away with them some times. Most last phases of each boss fight will have the boss turn invincible as he fires a last desperate barrage of bullets at you while you can't do anything but dodge them until he's done shooting, which is rather antithetical to the gameplay as a whole and does revert it to just call and response. Most phases of each boss phase are separated into a freeform phase and a swordplay phase where you can only use your sword and your gun is replaced with a charging ability which boosts your next attack if you have an open time window to charge yourself up. Comparatively, there's less freedom in these phases. It mostly centers around boosting yourself when possible and then moving in with a charge attack once the boss is vulnerable. While you can still interrupt attack chains, this is only really made full use of during The Edge fight which is the only sword-only bossfight of the game, where you can't simply always perfect parry for a punish and the standard window of opportunity of getting one hit in is like one after each attack chain, making boosting also a very tight ordeal.
Aside from other minor annoyances (which in a small game like this can be huge depending on who you ask), I still like this game a lot and am still striving to S-rank everything.