Except the hitboxes aren't anywhere near as fucked up in the nonUFO games.
My clipdeaths in UFO are because I'm used to the usual hitboxes and that I don't play UFO often because it is a terrible game. I'd rather play Cave's stuff then UFO.
UFO also breaks the shmup rule that all attacks should be dodgeable assuming the player knows what to do. UFO, like EoSD, can randomly just wall you, and you can do nothing about it.
And the power system.
And so many boss attacks are complete luckshit. Kraken Strike(Ichirn in general), Parasol Star Memories, Shou nonspells, Greatest Treasure, Radiant Treasure Gun, not sure about Byakuren as I never fought her on Hard, but I expect even more.
The bullet types used are harder to read. I can be sure I read it something correctly, then I get clipped.
There are only 2 things about the Shou fight that are even fun. Final nonspell and Vajra of Perfect Buddhism.