So what change to maplestory rustled your jimmies the most?

Potential was not bad when it first came out.
As long as we had the old damage cap, all potential did was allow the unfunded to reach it, by hunting for 3% or the insanely lucky 6% equipment drops from mobs. Cubing was only a shortcut.
When the damage cap was raised, though, and it suddenly became beneficial - and necessary, for certain bosses - to cube everything you have to Unique and 15%+, that's when the game became pay2win.

The patch I most hated was Big Bang. It seriously made me want to quit.

Big Bang was probably worse all in all, yes, but since the potential system was so real money centered in such an extreme way from the start I hate it even more. Big Bang wouldn't have been half as bad if not for how it worked in synergy with the insane cash grabbing.