This site most definitely delivers on the "fundamentals" it promises. Regardless of if you're planning on using a higher level engine like Unity or even something super simple like LÖVE, I would highly recommend at least skimming through. There's just no substitute for the low level understanding it maps out once you need to debug or do something tricky with 3D or shaders. Case in point: it clearly lays out camera matrix construction. Most libraries provide a magic function for this based on camera parameters, which is all well and good until you need to extract or modify the matrix itself.

This site was my bible for creating the 2D engine for Cat-Tastrophe: https://www.newgrounds.com/portal/view/861234