I'd played it a few times before in Saturn mode, casually using up my credit supply within the first 4 or so bosses and feeling pretty good that I made it through so many bosses before running out of continues - "i must be like 1/3 of the way through the game"
Wrong.
I just discovered you can set the saturn version to arcade mode to credit feed your way through it. Well, I did that, and I am extremely humbled. I was probably getting through 1/10th of the game previously. This game is a boss rush, there are so many bosses I completely lost count. I must have spent at least $50 virtual dollars credit feeding through the game. I can't recall having to put in as many coins to progress in any other arcade game I've played in the last 5 years.
I'm no shmup expert, but I feel like I'm above average. I can get through most cave games on maybe 3-5 credits with the deaths only really starting once I get to the final stages. I'm out of practice now, but I used to be able to get about 75% of the way through games like Battle Garegga and Batsugun on 1 credit. I'm very well acquainted with the 3d shmups on dreamcast like Ikaruga, Zero Gunner, Psyvariar, Under Defeat and the like and can get through those relatively easily. Doing things like leading bullets and visualizing paths through masses of bullets is second nature to me. I figured Radiant Silvergun would be similar to the dreamcast shmup library...
I have to say, none of my shmup skills seemed to help in Radiant Silvergun at all. This game is not like the dreamcast shmup library at all. In fact, I'd say that there is just as much dodging of random platforms, structures and ships, many of which cannot be destroyed before you would ram into them, as there is dodging of bullets. There is also an above average amount of dodging lasers, which differs from dodging bullets in that you can cross through a stream of bullets but can't ever cross through a solid stream of laser. There is also some of what I would regard as a cardinal shmup sin - that is having ships come at you from below the screen without warning, thereby killing you without warning if you are hugging the bottom of the screen (this just clinches it that one would need to do a lot of memorization to get through the game unscathed and eliminates the thought I like to have about arcade games, which is the remote possibility that "if only one was really skilled at the dodging, fighting or shooting mechanics of the player character/ship, he or she could get far into the game without big problems"). Despite the cool 3d graphics, this game actually feels like it has more in common with early (late 80s) shmups like Armed F, because in that game, you have to avoid many solid objects that cannot be destroyed, you have to adjust your gun a lot to find shots that work better in certain locations - oh and you also have to periodically fire backwards at enemies that come at you from behind.

I think I heard someone describe Radiant Silvergun (or maybe it was Ikaruga) as less of a shmup and more of a puzzle game. That's sort of how I feel after credit feeding through it. I can imagine what it might take to not dye as much as I did on my first full run through, but that would come primarily from intense memorization of the attacks that will be coming against me rather than enhancing my general shmup dodging skills.
The icing on the cake was getting to the final crystal boss where I can't shoot and the stupid crystal just keeps jetting out waves and waves of bullets for me to die on for 20 seconds. That wasn't the toughest part of the game, but I did see the continue screen at least once there. To find out that was the final boss (at least for my credit feed run through) just made it feel like a final cheap quarter grab.
Beautiful graphics, great music, really impressive for the hardware, but the game is tough as nails and seems to require extensive memorization. This might be the toughest "shmup" I've ever played.