God of War 3 was the main reason I decided on a PS3 for my first and only console this gen. Anything else is a bonus. And a very good bonus. Of course, I'd heard of this 'Metal Gear Solid 4' but I honestly didn't think it looked that impressive (the early trailers sucked)
Then I bought it because it got a 10 from IGN and GameSpot and a 94 on metacritic (should have been higher) and because the new trailer and gameplay demo looked amazing, and it now tops my 'favourite games of all time' list.
Maybe there will be another of those before GoW3 finally comes out. Don't know what it will come in the form of though.
I suppose because I have only ever owned Sony consoles (not counting GameBoy Colour) there is really nothing on the other platforms that could persuade me to buy them.
(Former) Lead Moderator and (Eternal) VGC Detective 
