Well, I think everyone already hit on my biggest game changers. One I didn't see though is paint shades pre-mixed for whatever you're using it for. I remember back in the '80s as a teen mixing those little square bottles of Testors paint for everything I painted till I found the Tamiya line. You mean I can just buy a bottle of German mustard yellow instead of trying to mix yellow and tan together!?!?! You could have knocked me over with a feather...
And it being acrylic paint too. You mean it cleans up with soap and water!?!?!