I think we can't talk about a game changer in any sort of definitive way. Most consoles had a contribution to the gaming medium and you can't really say "Online was more important that analog sticks" or "CDs were more important than jump starting the industry".
We've had the original Ataris, that breathed life into this hobby of ours, the NES that brought it back to life, the PS1 that brought it into the limelight, together with the N64 that brought us 3D games, the XBox that brought us the online services and the Wii that brought the casuals into our ranks like never before.
But in-between we've had rumble, graphic evolutions, realism evolution, analog sticks, programming techniques, story telling techniques, each console adding something new to the table in some way or another, be it memorable or not.
