One thing I didn't like about the Giant video was that it seemed to me that your character still took damage even when he went clear under the giant's legs behind him. Would there be any way to fix that?
That was meant to be an easter egg...the final boss is the Icon of Sin, not John Romero's Head. You can only see that with clipping cheats.
True, but Romero's head is what your rocket has to hit.
Also, according to the DOOM wiki:
A side note to this Romero-on-a-stick, when the player enters the main battlefield, he/she is greeted with an arcane chant spelled by the boss, which is actually a backwards-sounding dialogue that can be spelt as "Oremor nhoj em llik tsum uoy emag eht niw ot". If recorded and played backwards (making it the "correct" playback), it is actually John Romero's voice (distorted and reverted) saying "To win the game you must kill me, John Romero."
It's basically the same great game, with a new episode (which I enjoyed). Nothing revolutionary, at least now anyway, but a very fine, smooth game experience that feels as good as it ever did before, with the added bonus of suround sound and being able to play it widescreen on a big TV (should you have one). It's a pleasure.