XBox 360 in its early years, pre Kinect focus. Despite failing twice due to RRoD it had many great games building on to the momentum of the original XBox.
The only issue I had with 360 was the black crush due to Microsoft boosting the gamma for the entire system to make games 'pop' more. There were areas in Burnout Takedown that were almost completely black on my TV. Also some issue with the borders putting crucial HUD elements (like the current objective in Dead Rising) out of the safe screen area and thus hidden on my HD ready widescreen CRT tv. The system was made for PC monitors not for TVs at the time of release...
But that didn't take the fun away from Forza Horizon, PGR, TDU, Alan Wake, Dead Rising, Viva Pinata, Mass Effect, Kameo, Bioschock, Fable, Fez, Geometry Wars, Braid, TWD and Minecraft.
XBox One discontinued many of my favorite series and Series kinda feels pointless now :/ My least used system ever.