These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Goddamned Bats — The X-Box Arrange Mode adds numerous swarms of bats from every single direction, solely for the purpose of increasing the challenge.
Porting Disaster: The Xbox LIVE Arcade port runs in letterboxed 16:9 if you are using any resolution that doesn't have a 16:9 aspect ratio (i.e. a standard-ratio CRT screen), on top of the pillarboxing used to fit a vertical screen onto a horizontally-oriented monitor. So unless you have a huge widescreen TV or are willing to turn your screen 90 degrees, prepare to play in a VERY small screen.
Scrappy Mechanic: The coin chaining system. It would be more forgiving than DonPachi's Combos system, but it has one major concern: Your coin count carries between stages. So in order to obtain an optimal score, you have to chain the entire game—a broken chain can spell Rage Quit.