This isn't going back too far, but one thing that really bothered me about Half-Life 2 was the
E3 2003 footage.
See, two of the biggest selling points for me on HL1 were the interactivity, and the A.I. It was revolutionary to have interactive microwaves, or marines who knew how to take cover, return fire, and even flush you out with grenades if you just started taking potshots.
When I saw the level of interactive environment objects there were to take advantage of, I got excited. And when I saw the player use physics objects to block the door, and then the combine soldier that actually
tried the door twice, and then proceeded to
kick it the fuck in, I had to put on new pants.
Only later we learned how heavily scripted most of that stuff was, and the actual Half-Life 2 we got pretty much ditched any claims to enemy tactics or intelligent A.I. It wasn't bad, by any means, but I didn't really see any improvements.
Jam it back in, in the dark.