3. Oh I Didn't Realise You Had A Physics Engine
Valve we get it, you did good, pat on head and all that jazz. Having a physics puzzle is meant to draw you into the world more, it's there to make you think If this was real life what would I pick up and move and well done Valve you nailed it. There's a set of levels based around a canal, you have to get around on an air boat, a form of transport that is loud and boring in real life, let alone in this game. At one point you have to duck under the water to grab barrel and push them into a cage, which in turn raises a ramp for you to use to fly over a fence that's blocking your path. The reason I bring up the realism of this puzzle isn't for the floating barrels or physics of the jump, it's because as I would have in real life I looked at it and thought Oh for Christ sake, screw that and walked away for a long time.