In early 2010 I upgraded from both a battered PS2 (which had lots of hardware problems) and my last gaming PC (an already obsolete Athlon 64 with a low-end 2005 NVidia TNT 2 card) to a brand new Xbox 360; I also switched from a very old CRT TV to a flagship, 24-inch, 1080p Viewsonic monitor.
That said, the hardware upgrade was not as impressive as the change of ecosystem. Xbox Live blew my mind and rekindled gaming as my main hobby. Previously, I had seldom played online; now I was able to play with or against a growing number of friends. The controllers, the UI, the social aspects, the achievements and the 2010-2011 360 portfolio (Mass Effect 2, Red Dead Redemption, Halo Reach, Forza Motorsport 3/4) transformed how I experienced videogames.
Honorable mention: when I upgraded from my beloved Mega Drive to my first 486 DX-4 PC, back in early 1996.