Found this video really interesting as I have a relatively large backlog myself. Fortunately not nearly as large as this one.

Personally, I've only ever considered games I own to be part of my backlog, which makes my list much more manageable. That said, I have a large number of unplayed games on both Steam and GoG. So to start I've decided to play all my GoG games first (as that is still within reach). I've promised myself not to buy any more games untill all my GoG games are either completed or marked "did not finish" due to it not being my thing.