I've just started to play again at Doom3, with highest configuration and resolution; and except some *missing* post-process effects, particles, ...,it's quite hallucinating even nowadays. I like observing shadows in Doom3
I think Doom3 is just a bit *old*, and Doom2 is now into retro-games category (but still a legend).
So the 2 are not really comparable nowadays, Doom3 can still be completely immersive (cf realism) . Playing Doom2 is for 'souvenir', 'nostalgy' ... as myself I play regularly at Mario2 on GameBoy