I've seen other people say that this game being short is a positive as it means it doesn't overstay it's welcome, but personally for me with the game being so short, I feel doesn't fully explore the gameplay potential of a game where you control a hole. With other games I would be fine with them being super short and simple, but I feel like there's too much dialogue in between the levels that really halt the pacing to make it a smooth experience. Playing through the levels is like eating an appetizer where you're getting a tasty small taste, and then once you feel like you're gonna get a big hearty meal with more in depth mechanics, you get hit with the bill, and then you kind of repeat this for the entire game.

Super easy to pick up and play shmup with amazing graphics. A continuation of both the Dezaemon style and of modern shmup design that stays in a comfortable spot between gimmicks and bullet hell. Think Eschatos, Cho Ren Sha or some of ZeroRanger.
The game also has an extremely fitting soundtrack to the action. I've followed the artist for a long time but don't think they have worked on a shmup before.

Lots of pseudo 3D action going on with the stage design and bosses highly reminiscent of games like Kamui and Strania especially during the final stage.
Enemy attacks are extremely varied keeping things fresh for any kind of player. Despite the game being full of gimmicky attacks and surprises due to the great telegraphing it always feels fair to play.

Scoring system is also easy to understand and the game has gameplay modes for every type of player. Perhaps apart from a 'very hard' difficulty mode, as inferno is more like hard with restrictions.

In general a really nice package for anyone remotely interested in a shmup that's not in the bullet hell subgenre. But it's also one that also plays things safe to the point of encounters becoming a bit stale after your first playthroughs apart from the visual spectacle.

Some small gripes:

I think Stage 4 is a weaker point of the stage design. Fighting a big battleship cut to tiny screen segments removes most of the intensity you would experience if it was fought normally with the enemies or scrolling stacking up to overwhelm you. You can already see this by trying the included retro mode. Or comparing to 'enemy base' stages in other shmups like Garegga or Batrider. Ginga Force Chapter X does something similar but makes more sense as an extra stage.

The highest difficulty mode by removing Boosts has less gameplay mechanics for both survival & scoring play and only increases difficulty by restricting resources. It's still a fun mode but the reduced complexity is strange and the 'must point blank or die' thing only matters at the start of stages. Granted, clearing Inferno is still a good survival challenge. But it feels out of line with the rest of the game, comparing to an imaginary mode with 'Enemy level' raised to 4. Maybe in a future console release.

Scoring system is so simple that the game will probably be 'solved' in a couple weeks, with someone coming up with a basically perfect score that nobody will try to beat after the 1st month. As a result there would be no lasting score attack scene and people would quickly move to other games and/or not revisit Devil Bladet years later for improvements.

Flexible bonus enemy waves based on how fast you play ala Ikaruga would probably be a way to solve this, with it becoming practically impossible to be fast enough to get all possible enemies to spawn while maintaining max multiplier and not getting hit. There are some bonus spawns but only after midboss enemies once or twice in a game. Not using these bonus waves more seems like a lost opportunity as speedkilling enemies is something the game already does a great job teaching you to do.