I've always liked the idea of fixing mechanisms to go forward instead of finding literal keys
Really, the keys always so huge and colourful and left standing up right there on the floor in plain sight for Lara to pick up. I forgive the classic games for that because it was the '90s and everything was kind of colourful and tacky and stand-out during that decade
The gear keys in TR1 were really creative and something Anniversary did really right was including the giant mechanism as a way to explore. I also loved the crowbar, shovel and pole+hook items in the Last Revelation, although it wasn't always too clear what they were meant for.