I'm not exactly a bullet hell shooter connoisseur, but I really enjoy Project Starship. It uses a sort of procedural generation scheme that introduces random enemies and powerups each time you play. Still, the enemy fire patterns are predictable once you've gotten to know and identify them. So there's definitely a learning curve and a chance to do better. Some power ups seem more useful than others, so you might find the game easier or harder depending on what you get. Not sure what a serious player would think, but I really like it as a casual.
The aesthetic is firmly "early 90s arcade". When the game boots up, you can choose to add a CRT filter, which I appreciated on my 27" display. Then you are prompted to insert a coin (just hit the spacebar), chose a character (which changes the qualities of the ship and which character pops up at key moments) and pick either the easy or hard challenge. All the sprites are big and quirky. Enemies include frog legs, skulls, flames and a dozen different types of eyeballs. The projectiles are large and visually fill the screen. This is actually one of the few difficulties I had playing the game: it's not always clear where the hitboxes are. Music, sound effects and occasional voice clips add to the general sensory overload.
Besides the random waves of enemies and occasional boss battle, the game includes "Mad Events". These are announced in huge letters and then the game shifts to a game mode all about dodging. Instead of an enemy firing projectiles, the projectiles just appear and move in a fixed pattern. With nothing to shoot at, your goal becomes to survive for a few seconds. These seem unfair (I hope you got some shield power ups!) but are a useful change of pace.
I gather there is a local co-op option and various extra game modes, but I haven't tried those options yet. The new modes would require me to beat the game. Even on easy, this is a difficult game. For the most part, it seems possible to avoid getting hit, but I'm not nearly good enough or patient enough to get better. Even so, I'm enjoying the experience. It's not as frustrating as most difficult games.
Finally, this game is funny. There's an item called "TV Doesn't Work" that temporarily changes the screen to static. (It also clears enemies and bullets from the screen.) Obviously my monitor hadn't stopped working, but to the extent I was drawn into the fiction that I was playing a game on a CRT, it's an effective practical joke. This is the sort of visual gag that can only make sense in the context of a video game.