Depending on how low level the game got to the hardware, you could have some really weird changes. When I first started working on games, I was using mode 13h. What this meant was in order do set the graphics to 320x200, you had to set the CPU's AL register to 13h, the AH register was set to 0, then you called interrupt 10h, this caused the hardware to look at the registers and ender the video mode required. That's the crap you had to do for all softs of little changes.
Of and 640x480x15 bit color was fun. Like most VGA video modes, it was banked, you could only access 64k at a time. So you could draw to the top, then you had to call an interrupt, draw the next section, call an interrupt, ect. Each interrupt killed performance; lazy programmers would draw his sprites in the order they were created, switching to the proper bank wherever they sat. Good programmers would order the sprites by what banks they were in, and draw them as needed to prevent needless bank switching and loading the CPU up with interrupts.
Moving from a playstation to gamecube means all this crap has to be redone. Heck I'm thinking one was big endian and other little even.
