>>33432807Little details. For starters, they have to be designed differently to accomodate several colors rather than shades of gray, which is already a big thing since you couldn't just color old sprites and expect all of them to look fine..
In addition, they favored longer "hands" over round ones (for females, usually) and more distinct feet. Most NPC types got a complete redesign and many returning important characters got their own unique new sprites rather than generic ones, frequently with different proportions to boot.
So basically even though they were using a similar style for the same hardware, they revamped most overworld sprites (although some very few of them, like Prof. Oak, were just colored).