Xbox 360 (having the benefit of entering the generation late, in 2010):
-Red Dead Redemption, Max Payne 3, LA Noire and Halo: Reach for something like $5-10 a piece.
-Every NBA2K (from ´06 to ´13) for approximately $80, from a regretful Nintendo fan who was leaving Xbox when the NX rumors began. I had some of them from before, but sold them for more and got this cheap "complete package" as I am a big NBA fan.
-The Orange Box, used, for approximately $5. Even when I consider Valve´s games to be brutally overrated, I knew I was paying mere coins for a lot of content.
Xbox One:
-Doom (2016) was relatively cheap in my country´s marketplace: 666 pesos (roughly, $40, at launch). Great game.
-The Witcher 3 with all its content at $80 still feels as an incredible purchase.
-Both Wolfensteins for $14.
-Telltale Collection for... $40? I got lots of great stories for relatively cheap.
Honorable mentions: I got so many great moments from World of Tanks and Warframe that I felt obliged to invest in some microtransactions for both of them (some gold in WoT, some cosmetics in WF). Excellent free-to-play games.