One of the things I'm most guilty of is never playing the original Doom (or Doom 2) in their entirety. Part of that was because I didn't own a computer that could play it until 1996, and I was playing games almost exclusively on consoles anyway (and never got around to picking up any of the assorted, mostly mediocre, ports).
I own them all on Steam, and went and installed Ultimate Doom (along with GZDoom) after I started reading this thread. It's definitely still fun even 20 years on. Definitely a case where gameplay trumps all - you know it has limitations and even
with a modern port the game still looks like something out of the 90s, but after taking out a room full of enemies with a shotgun and finding a rocket launcher, you realize you don't care about any of that.
I still have my copy of Tricks of the Doom Programming Gurus and 3D Game Alchemy (both of which were books that contained instructions and tools oriented toward Doom and Hexen level creators). I also remember spending more time trying to create WADs than actually playing Doom by the time I got around to picking it up.