It's not a secret that Devil Blade's a great looking game. But I think that it's also easy to underestimate just how good its visuals are when all you're doing is playing - everything goes by so fast and things flow into each other so seamlessly that you simply don't get enough time to look around, much less think about the craft. And to me, that's a good thing because you are essentially getting a game that's so densely packed with great art that you will always notice cool new stuff if you try to pay attention.
With that said, even though most of what's in the game can't really be emulated because it takes an insane amount of artistic skill, I want to explore some things the game does right that everyone, me included, should study & learn from. These are more abstract, general (animation) principles, many of which are more kinaesthetic than purely visual.
Punctuation
Everything in the game is an event with unique animations, sounds and vfx. And this truly does apply to everything. It applies to things on a macro level (enemies have distinct fly-in and active animations/sfx/vfx), it applies to things on a micro level (almost every pattern corresponds with the enemies' body opening and closing different parts).
Even things like a huge laser bullet changing directions & the player getting close to enemies have their own sfx and vfx. When boss ships move on screen, they don't simply float around. They do an active banking turn in the direction they're moving in. Everything moves and shakes, the game feels alive and dense, even when not much is happening.
Here is a simple example :
Video version for reference
Pay close attention to the giant flame balls. When the boss shoots them out, there's a huge muzzle flash/explosion with its own sound. The balls start small & keep growing until they reach final size. Then instead of simply reaching final size & stopping, they produce yet another shockwave to emphasize their final state. After a little bit of a delay, they suddenly accelerate and move at the player. The fireball flashes to show that it's active, it produces a big shockwave and sound to signal its upcoming movement, and it produces a shockwave & light trail as it moves, to show speed. What could have been a simple set of actions/state transitions is made much more punchy by emphasizing every little change that happens to the projectile. This applies to a lot of special projectiles in the game, you might not see it unless you pay close attention, but you'll feel it.

Here is another example, except instead of anything happening to the projectile, the boss' body itself emphasizes different attacks. Before the boss can shoot, it has to adjust the position of its wings/cannons, making every attack & phase feel like a very distinct event. Even the boss' movement follows this idea - instead of simply floating, the bosses do these aggressive-looking banking turns that show which direction they're moving in.
Even the player getting close to enemies has such nice telegraphing that it often feels like the game has a lock on!
State transitions don't happen quietly, they announce themselves to the player. It follows fundamental principles of animation - exaggeration and staging. This kind of extreme approach to game feel is quite modern, and it's something Devil Blade absolutely nails. More shmups should follow this approach, because it makes the games feel ALIVE & VIOLENT. You can sneak in these elements that emphasize state transition anywhere, really the only limit is visibility.
Rhythm
Devil Blade is a very rhythmic game, most things from how the enemy waves work to boss attacks are quite segmented and discrete. The game is, for the most part, only doing maybe a couple of things at once.
Basically what it's doing is following the principles of staging in animation very closely, which helps give it that rhythmic, VIOLENT feel. For example, the enemy waves are very discrete, almost Touhou-like in how they spawn in. There's a quick spawn sequence that either gets killed immediately or leaves the screen immediately, followed by another spawn sequence doing the same. The game almost never combines elite & normal enemies (besides stage 4 which strays away from its rhythmical nature a bit) because this would create too much visual noise and mess with the telegraphing.
This applies to things like attacks as well - bosses shift & move around their parts for different attacks, but they almost always make sure that you have a bit of time to FEEL the body movement before the next attack comes out. Here is a concrete example :

The boss waits until its previous attack is almost done before opening its laser hatches. The hatches open VERY quickly making the action punchy (about 7 frames), there's a sound to punctuate it & then the boss lingers on that "pose" for 20+ frames before the laser telegraphing comes out. The initial action is fast, then you're given some time to process it, then the game throws the next action at you.
Unlike the first rule, this one is harder to apply because some shmups thrive on their chaos & overlap. However if you want really quick, punchy, violent feeling games that almost have a Warioware type of pacing, definitely look very closely at Devil Blade because it's a distillation of that style, even more so than the other top-tier example of this style of design - Cho Ren Sha.
The rhythm of the game is interesting as well but it's a little too abstract & hard to talk about - just try to listen & feel how different enemies/attacks spawn and see what you can find.
Motion
Last but not least, Devil Blade emphasizes motion in almost every way. Enemies have trails that serve as follow-through for their movement.
Bullets have nice, juicy, lengthy trails. Big circular laser-style bullets not only have trails but also get thinner as they speed up. Different enemies/bosses "sway" with their movement, or have really smooth, detailed turning animations.

Even a lot of the telegraphing (thin lasers that spin in a circle around the boss) is used to enhance the motion of patterns, because the telegraphing lines aren't static - they move. It's like Alucard's appendages in Symphony of the Night - everything is built to emphasize movement.
And of course, the movement itself is highly varied, with a lot of accel/decel states and enemies coming in from all sides and both the foreground and background. Really, the best thing to do to see how obsessed the game is with movement is to simply watch it in action. It feels AMAZING!
That's all folks
The game's audiovisuals are really impressive across the board, but the best part is that its (IMO) most effective elements, the elements that are most noticable during normal gameplay, are also the elements that are relatively easy to learn from. I can't make a boss that looks anywhere near as awesome as the ones in Devil Blade, but I can probably manage some nice looking trails! And all of this adds to what I call The Vertigo Factor which can be immediately noticed by basically all players even if they don't realize it, unlike say awesome detailed backgrounds that often get lost in the intensity of the gameplay.
If you want my overall thoughts of the game, just wait for The Electric Underground's review cause I'll probably agree with all of it unless he throws some crazy curveballs in there.

