I too think Doom's a fine game. I am a little curious about how you find it more intellectual? (and I don't mean to ask this in an offensive way, I'm genuinely curious). Doom did seem like a basic run and gun. But that said I can certainly respect you preferring it.
Oh, and if anyone remembers me and is wondering why I've been gone for so long... well I haven't been playing Marathon lately. But the CD is still on my desk by my computer, waiting for the day I will return to the Marathon/Tau Ceti and wherever else.