Like I said, I understand the programming reasons. They just don't translate well into functional game logic.
The wall blocks auto-attacks, Buckshot, and Bullet Time. A reasonable conclusion is that it blocks conal AoEs that use bullets. The fact that it does not block Corki's Gatling Gun is obviously very weird when you look at it from a logical or game balance perspective, and caused entirely by the way the ability is programmed.
The wall can block Seismic Shard and Whirling Death - the second of which is actually amusing, because it's something that wouldn't have been a projectile on older champions due to their early programming practices, but since he came after they stopped using some of the poorer techniques it is a projectile rather than a hitscan AoE or 'virtual minion' - but doesn't block Nautilus's ultimate. Again, it's entirely jarring: we've established it blocks things with a travel time even if they move on/underground, but because of the more dated methods used to program Nautilus's ability it becomes exempt?
The wall can block Flamechompers because an animator took the time to animate them zipping to their setup point, but not Caitlyn or Nidalee traps because someone got lazy and just had them magic themselves into existence rather than animating their placement. Again, it doesn't have a strong logical or balance foundation, and it creates this weird dissonance where "old and busted design" is apparently something you need to list as a benefit when talking about a character.
"Sure, Corki's kind of shit, but he was lazily programmed and doesn't interact properly with newer characters and their mechanics! 10/10, first pick/ban potential."
I mean, it's less a problem with the ability itself and more with how it's shining a spotlight on some of the shitty "leftovers" still stuck to some of the older champions that probably need to get updated to more unified programming and design standards.