I haven't played Doom 2 much, so the following comment is only regarding Doom 1.
I've always found the level design of both Marathon [0] and Dark Forces [1] much better compared to Doom 1. Both games had levels which in my opinion gave the player much better feel that they're in environments that could be real.
Both games were released around the same time as Doom 2. I only played a little Doom 2, because it bored me for containing so little story.
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