That's what makes it good though. The map itself is an enemy that needs to be "beaten" by having it's secrets revealed. The worst shooters are just about killing the enemies.
The chrono commando from Red Alert 2.

http://cnc.wikia.com/wiki/Chrono_commando

Convoluted? Any level in particular you have in mind? I remember getting a bit disorientated in some of the original Doom's levels but most of Doom 2's levels I found were easy to navigate (disregarding the monsters of course), with only a few exceptions like
http://doom.wikia.com/wiki/MAP04:_The_Focus_(Doom_II) <--- I never liked this level
http://doom.wikia.com/wiki/MAP05:_The_Waste_Tunnels_(Doom_II) <--- or this one
http://doom.wikia.com/wiki/MAP10:_Refueling_Base_(Doom_II)

In terms of navigating levels, I had a lot more issues with Duke3D's second episode's space levels.

Thanks, that would be why it looked familiar :) Never used the unit much though

I loved the Icon of Sin, and found it suuuuper difficult back in the day. Now knowing HOW to damage it other than BFG splash it's alittle easier.... infinitely harder/cooler than the final boss in the original DOOM.

And I liked Doom 3 but.. it went from a badass slaying waves of hellish minions to more of a survival horror game that didn't quite grab me like Resident Evil, Silent Hill or other franchises around that time.

PS. Tricks and Traps might be my favorite (or atleast most memorable) level ;)

Icon of Sin can be a real pain, especially if you don't know what you are doing.

People don't like Doom 3 as much because it tried to be more like System Shock 2 than Doom 1/2.

mediocre gunplay combined with the the fact it utterly failed in "horror" aspect. The jumpscare enemy closets got old in the first hour of the game.

Funny how you know why people "don't like Doom 3" and can speak for literally all of them. Well, I didn't like it because it was the typical pathetic Id crap that all their games have been since John Romero left. An absolutely dire corridor shooter with zero innovation and absolutely nothing like Doom 1 or 2: a bit like all of their other truly dire games ... speaking just for me of course.

Have you seen the final boss of Dangerous Dave 2? Well, the devs can't use the same idea twice. ;)

IDCLIP was so much easier to type than IDSPISPOPD

*punches things behind wall in face with fist*

I haven't even played DoomII since the 90s, but the boss is pretty memorable and for me that means it was good. But then, they're pretty great games (I even like 3 quite a bit, I don't understand all the hate. Doom 4 looks pretty exciting to me, waaaaaayyyyyy more than Fallout4, by shittons, even though the color-palette looks a bit lame.)

I like how you had to figure out what to do and that it wasn't an adrenaline packed DPS/avoid damage challenge like so many boss fights are. It's kind of like "yeah, so what you're here? Are you going to kill me already please? if not I'ma just keep doing my evil thing, but, it'd be nice if you stopped me, I won't stop you from stopping me at this point, though here's some half-enthused attempts *spawns mobs*."

I liked Quake 4 quite a bit. Too bad it never had any more.

Quake 4 was another good game that GOG needs to get. Here is the wishlist!

But doesn't GOG have a ton of Activision games?

I remember back in the day being fairly unimpressed by Icon of Sin (and Spider Mastermind, since I thought the Cyberdemon had a cooler design, took more hits to kill, and did more damage). But that Brutal Doom version looks awesome, I must give that a try. Right now I've finished playing through the vanilla versions of Doom and Quake with the classic control schemes, and halfway done with Doom II so far.

Hmm, I thought so too but I just checked Steam and it's published by Bethesda there:
http://store.steampowered.com/app/2210/
That actually gives me some hope for Heretic II coming to GOG, maybe it needs their touch like Battlespire and Redguard did.

I'm so sorry there's no cover to hide behind, and no health regen at all.