Single Most Iconic thing from Doom

[Acid]

Let's have it. What made Doom...Doom? Instead of OH, MONSTERS or OH, DETAIL. What would the SINGLE thing about Doom that sets it apart from other FPS's? Speed? Flow? Customization? Puzzles?

A little reaso behind it wouldn't be bad.

[Krispy]

Modifyability.

[glenzinho]

Shotgun

[Lila Feuer]

So goddamned easy to change and add everything I want to the game, especially with ZDoom. In addition to never again being annoyed by shitty sprite/sound replacements in a custom WAD, I've been ripping skies, statbars, custom palettes, sprite replacement alternatives (e.g. Eternal Doom Imp, PSX Final Doom SSG, blood splats from Heretic/Hexen) and music from my favorite WADs for personal use with any maps I play that either don't have new content or just to mix things up.

I wish other games were this easy to edit and implement new things. Since learning DECORATE (and being unable to leave anything alone) it's also allowed me to further modify ZDoom mods that I like to my preferences and experiment with my own personal brews. And due to the PK3 structure, I can easily load several files I want to use all at once without hassle of drag-n-dropping twelve things. Doom has fantastic mod capabilities and I love it so much for that. The ease of use cannot be underestimated. It's more or less the kinda shit I wish I could do with Doom as a kid (like re-use some cool new graphics or music outside of a WAD I like with any other WAD now), and now today it is completely possible.

[Grazza]

Infighting.

Adds an extremely important extra dimension to the gameplay, as there is a much greater reward for smart play than there would otherwise be. It also means that the player can beat what seem like insurmountable odds - despite being vastly outgunned and outnumbered, some deft footwork can pretty much enable you to annihilate an army of hellspawn with a few pistol shots.

Take away infighting and you have a totally different game.

[Lila Feuer]

Infighting is almost in every id game. It is, however, a feature I feel that was sorely missed in BUILD engine games and newer.

[Chubzdoomer]

Soundtrack and pacing. I think they go hand-in-hand.

[Technician]

Speed and intensity. Modern shooters just don't have that breakneck mechanic anymore.

[_bruce_]

Style.

[printz]

The Icon of Sin from MAP30.

[Stroggos]

The corny B movie effects/style that got it into so much trouble back in the day. Because I have a bit of a warped sense of humour and it was really the first game I saw with this sort of demented/demonic style. I was playing DTWID earlier and the style still manages to make me smile...

[DoomUK]

Just being Doom made Doom Doom. It's hard to pick out a single thing that epitomises it.

[Kira]

The techno-dungeon feel.

[negke]

I'd say the BFG. It's something that pretty much everyone knows or recognizes, even if they don't play Doom or never had.

Technical features, on the other hand, can't really be considered "iconic" in the true sense of the word. Though the OP question isn't clear about this, and well, it's just another one of those threads, after all.

[Phml]

Freedom of movement. That fast player speed with reactive turns coupled with the relatively slow moving enemies and projectiles (and that it is, for the most part, projectile-based rather than hitscan amplifies your superiority). The *lack* of jumping and of true 3D architecture, I think, also helps, because having to care about only two dimensions makes movement much easier to manage, more accessible.

[Harmata]

The name itself.
Edit:oops, that's the answer of the question "Single Most Iconic thing from Doom", but what sets the game apart from others, i'd say it's incredibly well thought out arcade gameplay.

[40oz]

The Doomguy's HUD face

[Maes]

The Unofficial Doom FAQ v6.666

[elic]

That there's no guy yelling at you "RAMIREZ! GO TO BURGER TOWN AND SHOOT DOWN THOSE HELICOPTERS! MAKE SURE YOU GRAB THAT JAVELIN IN THE CLOSET NEXT TO THE BATHROOMS! WHILE YOU'RE AT IT GET ME A BURGER WITH FRIES!" etc.

[Xaser]

[PRIMEVAL]

Everything

[Maes]

DOS4GW.EXE

[Dco16]

Deathmatch.

[dew]

IDDQD and the golden eyes

[Krispy]

Fiend said:

Deathmatch.

That too.

[Gez]

This.

[Maes]

INSTALL.EXE, where it all really started from.

[_bruce_]

40oz said:

The Doomguy's HUD face

Still love the HUD face today... so well drawn.

[CODOR]

Non-orthogonal walls, after having played Wolf3D for like a year and a half...

Xaser said:
http://www.classicdoom.com/maps/d1fpvs/e1m1.gif

Needs to be 320x200 :-)

[DuckReconMajor]

Great graphics and the advancedness of the engine at the time. Even though the Doom community today likes to look down upon people who hold a game's graphics to a high standard, I'm sure back then Doom was the go-to game for "graphics whores".