I think Valve learned a ton about game design between Half-Life and Half-Life 2. Half-Life 1 pulls a lot of "gotcha" moments that you just have to reload your save to get through, whereas Half-Life 2 actually make sure to have teachable moments so you know what to look out for, and here's my favorite example. Half-Life 2 introduces you to a sniper enemy right after Ravenholm by having a traceable laser pointer that's shooting escaped headcrab zombies. The sniper is concerned with them, not you, so you have time to be aware of the threat and know what it looks like. Half-Life 1 introduces the sniper enemy by having you round an ordinary looking corner and get shot in the back. After reloading your save, you can squint at the hole in the wall in that alley, knowing it's there this time, and say to yourself, "Yeah, I guess that kind of looks like a sniper's nest."
The gimmicks that you refer to in Half-Life 2 are, I think, phenomenal examples of how to properly pace a video game and make the game memorable. While Gordon Freeman is a nothing character and more of a focal point for everyone else in the game to talk about, those characters are good, well-written characters.