Thanks for the feedback
I actually considered the 8-bit Xmas carts, I went through all the years. I was going to add that but I decided not to last minute (didn't want to get too offtrack with the guide). I guess it doesn't hurt to add that title though since it is shmup oriented. I'll pop it back into the "fixed-screen, NES homebrew" section.

PS: I had one in my shopping cart back in 2008 but decided not to get it. They go for like $500+ now?
In regards to the other comment about differing regional titles, I considered that too, but scrapped it for the same reason mentioned above. For the unaware readers, having redundant japanese/american titles can be confusing/misleading (for example seeing a game like Shin Jinrui: The New Type on the list, just to find out it's Dino and Riki on NES). However, I do see a need to add games with significant regional differences, like Gun Nac (JP) for example, which was censored for the US release. I'll make mention of this in a future update (as mentioned in the guide, this is still being worked on).
I think you're right about the shmup elements, that makes sense. I'll move The Guardian Legend to Vertical, with mention of overhead stages. I'll also make note of the Super Star Force overhead stages. Xexyz to me still feels more platformer than pure shmup (kind of like WURM), it's a tough call. I'll update the list for the other changes though.
Cheers!