Can't wait to see, I loved unreal tournament 

I'm trying to keep in mind advice I've heard from various places. The most helpful of which so far has been from Daz during one of his videos on Custom Gamer, where he says it's best to put detail in places the player can't get to, such as ceilings, or high on walls. I certainly have a lot of space like that to work with, so I started brainstorming.

If I stay with the metal theme, I think it'd be easiest to preserve the feeling of Stalwart with a cargo, storage vibe. I have lots of areas I could add bays, racks, and shelves for flavor and fun yet functional lighting. I figured I'd start with the ceiling.

http://db.tt/x49W5N9n

Then I thought it'd be cool to have in-wall bays, something to make them feel less flat.

http://db.tt/8WgAOIJ9

Probably not best to have it right under the rack. I think I'll make it run the length of the wall. There's a clipping brush to stop players running up into it, but I don't like using those. I think it's better to build a way to keep players out, or do something else to communicate that the area is for decoration, which feeds back into the advice of keeping detail out of arms reach. I may make the in-wall bay double-decker, move it out from under the ceiling mounted one, and put items in it that were previously on the floor. Maybe an alcove. Still thinking and experimenting.

I'm also considering a medieval theme. I usually use torches or fireballs for temp lighting because it's easier to visualize once you get in game where shadows are coming and going from when you can see all light points. The fire is kind of growing on me, and I have some ideas to make sure of the awesome stained glass textures wake has. Like I said still thinking. 

Make sure to check out Kell's Knave texture wad. It blends between rusted metal and medieval quite nicely (a bit q3ish in that regard) 

I had forgotten how boring the layout of Stalwart is.

I think Knave is a bit of an overused texture set at the minute (even I have a knave map on the go). But it is probably much better to have that than the current set, I probably would have gone with a base theme. You know what would rock? If someone made DM-Peak. 

it's best to put detail in places the player can't get to, such as ceilings, or high on walls

Does he give a reason for that? What video did he say it in? 

He was talking about a map he was making that he gave up on, called "Factory".

http://www.youtube.com/watch?v=k7FZAuWfNNg

At about 11:45. If you want to have fun with geometry, put it up high or otherwise where the player can't get to it. The gameplay area should be functional and apparent, and having superfluous geometry/excess props and fixtures where the player has to navigate, or consider navigating, makes the area less immediately understandable.

Of course if your goal is to make it less understandable or to make the path not obvious, then it doesn't apply, but if you're just trying to add detail it's probably best/good to do it in a way it can't impede/confuse/mislead the player in any way. 

extrapolation on the theory is mine, those aren't his words exactly 

It sounds reasonable, and I mostly agree for abstract games such as Quake. But if you look at the world around you, detail is usually all round you. 

It's not realistic, but it makes a lot of sense for gameplay. Realism alone is not a desirable quality. The most important thing you should consider is for your games to 'read' right. Players and monsters should be easy to discern from the background. So when you put in the eyecandy you add it in places where it adds to the visuals without interfering in the gameplay oriented visuals.

Detail is a misnomer by the way, it really should be 'contrast' or big changes in luminosity. You can do a lot of geometric detail, if the lightness stays within acceptable range it should look fine.

For instance, a black and white checkerboard texture on the floor will start competing for attention with other scene elements. You want to focus player attention to where it matters. 

but it's still excellent for Quake :) 

In a Quake DM map, players can reach pretty much every spot as soon as they have explosives.

So ceiling detail isn't out of the way in a Quake map.

And if you clip it off, players are gonna ask why they can't get to that nice camping spot.

This is probably why the original maps are relatively bare, as are most Q3 maps. You give them a grenade launcher, and they can get everywhere. Hence I usually try to make detail useful for gameplay at the same time. 

Not sure I agree. I think Romero just had a fetish for ceiling detail. It's also a logical spot for complex beams, lighting, etc, and, if you build so much detail that the player COULD go there, why not just make it a secret (ala near the end of e1m2)?
This is all assuming it's indoors. Wall detail is good but requires a lot more clipping so as not to interfere with gameplay.
Floor detail - who's done it?

Not that I've put a lot of thought into this. My approach has just been to entertain the player visually by having large/outdoor areas visible, rather than detailed indoor areas. 

Is something I love to do... 

But I enjoy good outdoor detail more than indoor. Especially in a game like Quake where anything goes. You can design whatever kind of weird, off the wall structure you want, and it'll fit right in. Cathedrals with cool spires/roofs, castles with crumbled walls and bulwarks/battlements, military bases, prisons, depots, it's all fair game and the player will eat it up. I know I do.

I especially love maps that appear to be a place in a larger environment, like with surrounding cliffs or with vistas that give you glimpses of areas off in the distance. 

I'm always torn with that... so you start making some area that is just for decoration, to make the map look like more than it is. then you realize it's cool, so you make the player able to reach that area. now you need to make another place outside of the map to make it look bigger than it is.... rinse and repeat. :( 

"an attraction like that of viewing far off an unvisited island, or seeing the towers of a distant city gleaming in a sunlit mist. To go there is to destroy the magic, unless new unattainable vistas are again revealed." - Tolkien

The idea of a map taking place in a larger environment is so appealing, but it takes so much effort to build it, and I have exactly the problem Necros just mentioned / I am unfortunately lazy. 

to clarify, I was only talking about deathmatch maps. 

Personally I like the parts where outdoor/indoors meet. 

The main point I was trying to make when talking there was that it can be very frustrating to navigate around a cluttered area with lots of stuff needlessly getting in your way. Even more so when you are in a combat scenario and you are getting stuck on little details sticking out of walls etc.

The space should be functional for its purpose.

There are times when this can be a good thing, for example if there is no combat and you want to make the player feel like they are exploring somewhere new where no one has been before, then placing things in the players way can help with that. If the player has a clear route through an environment then it can sometimes feel sterile.

This mostly stems from the fact of playing so many source engine custom maps where OH LOOK, A ROOM FILLED WITH BOXES IN MY WAY AND ENEMIES which gets annoying very fast ;) 

another purpose for clutter can be to slow down the pace of the gameplay (obviously in non-combat areas). you may want to stick a pile of crap in the player's way after a big fight to kind of calm them down. 

That reminds me of Black Mesa where I would constantly get stuck on props lying on the floor. I had to crouch jump over everything with the abysmal jump height (eventually figured out it could be tweaked and all was well).

They also put knobless doors everywhere. I knew I couldn't open them, but for some reason I always tried on the odd chance I might hit some secret room. 

http://spawnhost.files.wordpress.com/2013/09/collabmap1.jpg

http://spawnhost.files.wordpress.com/2013/09/collabmap2.jpg 

This is a Quake 3 map using Starbuck his Base set remakes. Lighting isn't final.

http://imgur.com/LjiqZWM

http://imgur.com/aerhkpY

http://imgur.com/3FlbRvg

http://imgur.com/Vjq1w6P 

I like it but as I said there, if you are going for q1 look, I think lighting should be more monochromatic. If you dont mind the q2 comparisons, its fine as is. 

Looking good. The Quake vibe is within grasp for sure. Since the textures are so nice and the geometry is on point, I'd say that making sure the lighting comes out with just the right amount of harshness will decide if it feels like Quake1 or not. The lighting needs to be good, but just crude enough it retains the lo-fi oppressive feeling.