Difference between PAL and NTSC on something like the SNES and Megadrive would be a decrease in speed in games, as well as the black borders in PAL games since PAL uses a higher resolution than NTSC.
I don't always notice the black borders, cause I never usually compare PAL vs. NTSC between consoles, but I do notice how slow or fast a game can be if not coded properly for whatever region.
Take Shadow of the Beast on the Megadrive. The NTSC version runs faster than the PAL version due to improper coding, making the game very difficult to play. Watch laffer's SOTB platform comparison to see what I mean.
Another example is Sonic the Hedgehog on the Megadrive, and the PAL version is slower than the NTSC version because of, you-know-what, bad coding.
Here's the difference between NTSC and PAL of Sonic on Megadrive: