Games today try to encorporate qualities from many different genres so the line gets blurred once in a while. Most games today have some sort of RPG or action element to them, but we are able to decifer that Soul Caliber 2 is still a fighting game and Madden 2005 is a sport's title. I think when defining a game, we have an innate sense of what it is. We have prototypes in our mind like strategy = chess or command and conquer, rpg = dungeons & dragons or final fantasy, strategy rpg = shining force, first person shooter = doom, etc.. and we compare the game we are currently playing to the prototypes in our mind and decide which ones they relate to the most. Subconciously over time we lump a bunch of new games into these different categories in our mind and we then have more games to compare the even newer games to. So yeah, I consider Ratchet and Clank a platformer. It's qualitites are most reminiscent of games like Crash Bandicoot, Donkey Kong 64, Jak & Daxter, or even Mario 64 in my mind, so that's where it gets filed. If you read magazines, you'll notice some pictures have Sly, J&D, and R&C in the same shot, all those games are different, but they have some kind of air to them that let's you know they are the same genre of game.