In addition to battery life, colors, and screen size that others have mentioned, I think the weight reduction on OLED when I upgraded was actually the biggest thing that shocked me.

It’s not immensely different, but if you use it daily, it’s lighter enough than the original model to make a noticeable difference and just makes playing so much more comfortable, especially for longer periods.

I would not have expected the weight reduction to be this big a deal, but it really is for me.