What a coincidence, I've been playing Doom 2 for the first time over the last couple of days. I've also recently replayed the first, but I had actually played that back when I was in primary school (behind my parents back of course).
I'm surprised just how much fun it still is and if you use something like ZDoom [1] (which I have been) you can literally just run the binary with no setup and it runs flawlessly on a modern system.
One thing that really stuck out to me as I've been playing it is that there really isn't anything from modern shooters I miss. I'm not trying to diminish the work that has been put into AI, Physics, Graphical fidelity etc, but what does it say about the genre when you can remove all the innovations over the last 20 years and it's not any less "fun"?