Funnily enough, my opinion is almost exactly opposite to your one at least in the OMG factor of the enemies. For me, it's more of an ohmygod, look how blurry and indistinct they are (despite being larger graphics), and why is the cacodemon like a cartoon monster with its handcuff chains and over-sized vampire fangs and why is the pinky demon giving out teletubby "big hugs". As for the sounds, they sound very contrived to be "woooo scary" by being all echoey and bassy. The textures are grainy and messed up looking and I find many of the levels quite frustrating. The music... well, OK, I like that.
I'm not saying it is a bad game - far from it and it has some very good features, including coloured lighting, 3D effects and so on - but I just don't feel that it fares particularly well when being compared to the original and, personally, I don't like the graphical style anything like as much as the PC original.
I agree that it is a stepping stone between Doom and Doom3. Doom is one of the best games ever made. Doom3 is a pale shadow of its grandfather that failed to deliver on so many fronts. D64 being good, but not as good as Doom means it fits quite happily between them.
 typo - omission of a "not" [/edit]