Found this channel, Threat Interactive, some time ago and have been watching the videos. He uses debugging tools to go step by step on how each frame is generated, explaining bottlenecks, things that reduce performance (like computing some stuff more than once, out of order, etc) and things that make the final frame look bad (usually bad anti aliasing)

The dude gets very mad about the state of current games' pipelines, mainly due to how Unreal and Nvidia have fucked things over for their profit - and really, when we take graphics from today and compare with games from 2016, it's easy to see downgrades in quality AND performance.