My apologies for my communication dropping off in the 2nd half of the month. I know I missed the podcast, but for posterity thought I'd finally add my thoughts.
I really never got through the boss of Stage 3 on the first credit, my best score was around 14mil. I did a bit of practicing on it, but it's a lengthy boss and I never got it perfected. Not too surprising that Raiden IV felt a lot like the first Raiden given the mainline naming, but I didn't get bored of the first stage as much as I did with the original Raiden. But they both felt pretty narrow in terms of routing options.
In terms of the Summer of Raiden on a whole, I really enjoyed the theme, and really loved Raiden Fighters. I've heard the sequels are even better, so I'm interested in getting to Fighters II or Jet sometime.
You definitely missed getting in for the podcast, but thanks for sharing your thoughts anyway! I slept on Raiden Fighters WAY too long, so we'll have to try and squeeze one of the other Fighters games in sooner rather than later. And don't worry about dropping off - this is all about playing as much as you can or want to, and however/whenever you can participate is great. We're all busy adults with full lives, so it's not always possible to join in, or even participate much when we do.