I was practicing a bit of Soldier Blade over the weekend, trying to focus on just one level at a time and learn the layouts. It's hard to compare shmups over a long span of time, as even minor skill improvements can reframe an entire game. But looking at just the few I've played recently (Axelay, Cho Aniki, R-Type, S&P if you want to count that), two things stand out about Soldier Blade.
First is that it's really fast - not an original or particularly interesting revelation. But compounded with the 45-minute length (longish, compared to the 30-min norm), it means tons of content spewing from just a single loop. Not that I've taken the time to count waves, but it at least feels like three of R-Type's levels could fit in one of Soldier Blade's.
That said, the excess is packed with a hefty supply of popcorn*. Admittedly, Axelay and R-Type are self-consciously stripped down games, and Cho Aniki is... something else in terms of level design (not good), so Soldier Blade's ratio feels closer to average. It's not even bad popcorn - most of it comes at weird angles that make your weapon level relevant (always a bad time to have Blue 1) - it's just that at the rate the game moves, it adds up quickly. It isn't afforded the same level of variation as the primary waves (nor should it be if it needs to remain low-engagement), so you see the same couple waves in every level.
A third note that I knew already, but contributes to the same conclusion: the x-axis orientation of some enemy patterns is determined reactively by the player ship's position. That is, if Soldier Ship is on the left half of the screen, a string of popcorn may stream in from the top right corner, but if positioned on the right the same wave would come in from the top left. Since this behavior is specific only to certain waves, the stage doesn't just flip-flop - relative enemy positions will actually change.
What this adds up to is a game resistant to idle memorization. I don't consciously commit shooters to memory (I don't know that I could), but after a degree of practice it becomes instinctual. With high speeds requiring high response time, enemy spawn points derived from player position, and a relatively limited weapon swap, Soldier Blade places value beyond the obvious on knowing what's next. Yet it readily defies the patterns that make this knowledge a subconscious product. The layout density creates an excess of information to store. The uniform popcorn puts just enough space between distinct encounters that the concatenation of "Wave A, then Wave B, then Wave A, then Wave AB" requires an investment of active memorization (while fighting popcorn: "Wave C came last, Wave C came last, Wave C came last"). And the reactive spawning does more than mix things up - it adds pre-wave activity to the necessary data set for layout prediction.
It's an effect well-coordinated with Soldier Blade's presentation and balancing to make the game feel especially lively and engaging through repeated plays, moreso than just being "fast". Particularly satisfying is seeing this kind of spontaneity evinced through techniques not reliant on randomly generated elements or structural flattening.
*"Popcorn" is a term used by shooting game enthusiasts to denote waves of one-hit-point enemies that typically don't fire projectiles. For example, the first few waves of any given stage of Gradius. Popcorn isn't meant to defeat the player, instead it keeps them lightly engaged while creating some breathing room. Think of it like the foam packing peanuts in a shipping container - not what you're after, but necessary to fill out a stable, symmetrical structure. I came up with that metaphor because I thought the packing material was called popcorn, then as I wrote it out I was like, wait.