Until you play the games, you don't know. End of debate.
I generally assume what the developers themselves say to be pretty accurate, don't you? Based on that, I don't think Doom 3 is anything special. I'm sure it will wow some, and the graphical advancements are important. But I place gameplay above that, and based on what the developers of both games have said I'm more interested in HL2. I'm assuming iD's entire design philosophy won't change between now and early 2004, but hey, I could be wrong ...