I think one of the main problems last generation, especially on Xbox was that it felt like it was a one trick pony in terms of the games it offered. Gears, Halo, Forza, rinse and repeat. It was an FPS dream but the diversity wasn't there. And when titles did appear that broke the norm for the Xbox, they just didn't sell very well.
It's the main reason I switched from 360 to PS4. Nothing really to do with the supposed power difference, more to the point that when I owned a 360 I felt like I was missing out on so much that was on the PS3, and all I was being shovelled was the next Halo, the 4th instalment of Gears, the 5th version of Forza or whatever.
Put simply, I wanted more choice this time around than running around a map with a gun which I'd seen countless times before but with a different name on it.
So yeah, I don't think necessarily that Sony is the bigger brand, but it IS known for being more diverse and offering up more choice in terms of games you can play.
PREDICTIONS FOR END OF 2015: (Made Jan 1st 2015)
PS4 - 34M - XB1 - 21m - WII U -12M
