Okay, so before I get in to actually talking about the picture, I just wanted to mention that I've categorized the comments based on what I'm talking about for consistency (since I tend to jump topics frequently).

The underlined text is the category I'm talking about (lighting, design, composition, decals, particles, overall detail, etc.), the bold text is the topic being covered in each category (critique, useful pointers, future references and such), the colour of the category corresponds with the colour of the markings I made on your screenshot, and the italicized text is stuff that, in my humble opinion, is the most important stuff.

Actual Critique

Lighting
Let's start with things you did right: You tried to light up the entire room and leave no giant, dark shadows - that's excellent that you did this intuitively.

Unfortunately, your method of lighting up the room made the corridor look like a thousand burning suns were poured on to the floor (labelled 1 in the picture). Those lights are incredibly strong! There are a couple problems with using that many candles:

1. They look pretty nasty from this particular angle
   
2. The number of animated flames causes a lot of lag on most computers
   
3. The number of lit candle animations is probably causing your computer to lag too
   
4. There are ways that are a whole lot better to light up a room like that (which I will discuss later)
   

Instead of using a million candles, you can use a few and then attach pointlights to them - this increases the area they light up, but doesn't give that 'sun shining out of god's ass' effect. I'll discuss how to do this under Useful Pointers later.

On the topic of pointlights/boxlights/spotlights, it looks like your map is generally lacking them. It looks like you might have one white pointlight above the door with curtains (and several bright red ones much further down), but the general lighting is provided by the candles. There's a good reason why you should actually use boxlights:

See the dark, outlined portion (labeled 2)? It's completely pitch black. Unless you have a black-hole hiding out up there, the brightness of the room would flood that corner too. Light bounces off of surfaces (more on shiny surfaces, like mirrors, than on rough ones) - you can see this if you hold a piece of blank, white paper against a dimly-lit object and shine a brighter light on the paper. The object will brighten. This same kind of effect should be visible in your map.

The easiest way to imitate this kind of effect is to have a boxlight in your map. Just one boxlight, should be large enough to cover every single part of your map - not just one room - the entire map.

Speaking of boxlights and pointlights and lights that don't cast shadows, the area (outlined with at great big 4) has red light leaking through the walls - or at least that appears to be what's happening. If that is light from the red room, try moving the source of light away from the wall a little bit - you can rotate candles and it will have the same effect (the lights attached to candles are offset for this reason).

Aaaand now on to area 3. The lighting around it seems very, very white, but the light coming from the candles and lanterns has a much more yellow-y tone to it. Since the room on the far end is red, I'm assuming you know how to change the colour of pointlights. You can either mess around with the values until you get something similar that looks good, or you can try connecting the pointlight to one of your lights.

Lastly, you could do some more with sense of lighting direction. I get the feeling that, based on your picture, you want the player to be drawn toward the bright red room. The colour does a great job already, but you could also have the light leaking through the door (not the walls) and casting some really cool shadows (if you use a spotlight). If the area in the hall outside the door is relatively darker, that contrast between the bright red room, the spotlight, and the outside with the shadows will also draw the player towards the room. That said, the corridor/hall shouldn't be pitch-black or too dark either - perhaps just gradually getting dimmer/redder as you progress towards the end.

Particle Systems
You added particle systems, thank you! They're really good for adding detail without having to add objects.

I believe the particle system in front of the door is the dust_falling one (or whatever it's named), right? Well that one (labeled 1) is very opaque in contrast with the rest of the room. Sort of like light, dust will spread throughout a room. Some areas of the room will have thicker amounts of dust/fog (sources like cracks in ceilings), but it all spreads out a bit. Aside from your one dust particle I noticed, the air in the room looks very, very clean. There are several ways to mitigate the contrast:

• Add more particles to make the air look dusty
  
• Lower the alpha of the dust
  
• Change the colour of the dust to blend with its environment better
  

Another reason to change the colour of the dust is because it stands out and doesn't look very natural as a bright white.

Another little thing about particle systems before you go throwing them all over your map: Be careful of their placement. The area labelled 2 in the picture shows a very sharp cut-off between the particles and the ground. These kinds of cut-offs make it really obvious that the particles are not 3D and can (with picky people :p) break immersion. Easiest way to do this is to set the alpha of the particles to 50 (yes, you can do that - shows up as 1, but it's actually 50) so that they're completely solid. Much easier to check placement like that.

Detail Work
Not bad there, good sir! I can tell you were making an effort to have the whole area look detailed in some form or another instead of lazily slapping a few candles and walls down and saying "ta-da!". Give yourself a pat on the back for me :D

Now then, there are some things that you could do to make it a *little* bit more interesting and natural looking. Does everything have to be completely perfectly straight and lined up (Hint: the answer's 'NO')? I would suggest turning off the little magnet thingy in the bottom left-hand corner of the level editor, that way objects aren't snapped to the grid - meaning you can give things subtle rotations (between 1~2 degrees).

(In my ever-so-humble opinion,) The best thing to do is remember that humans made everything in this game-world. Someone placed those statues there, someone hung the mirror and smashed it, the drawing probably fell to the floor, etc., etc. - it would be weird if people had everything lined up on perfect grids with everything at 15 degree angles.

So let's examine the mirror/painting frame example a little closer: someone hung it on the wall ages ago - it probably looked pretty decent at that time, maybe it was perfectly straight. At some point though, something/someone broke the glass on it. Since the owner of the place didn't care to take it down, would they have bothered to re-straighten it after it was broken? Probably not. Basically, what you're going for is making your maps look like someone lived in there - rather than making it look like a haunted house prop from Disney World.

Another example of this is that floor: there's stains of pink liquid all over it, undoubtedly other stains occurred over that rug's life-time. Since the owner didn't care to clean that stain up, they probably didn't make much of an effort to clean the dirt off the rest of the rug either. Speaking of the rug, it's stretched a little bit too much; the textures are starting to look fake. I'd suggest making it a teeny tiny bit smaller (maybe scale down by 0.15) so that it's not actually touching the walls on every side.

Now on to that large hallway: too many statues, too many candles. Because the statues are all exact replicas of each other (due to the nature of games), the pattern is painfully obvious and, well, a little boring. Instead of having 10+ statues sitting along the edges, maybe delete half of them and place candles in-between the remaining ones (some lit, some unlit to make it more interesting). Alternatively, since that room is huge (and the ceiling is bound to need support of some sort), you could place supporting columns between the statues.

Screenshot Composition
The screenshot itself has a nice sense of direction, the angle allows for details to be included, and all-in-all, it's very nice. On the other hand, you've set up both the hallway and the corner with the painting as focal-points. I've drawn in a "rule-of-thirds" grid (in grey).

The lines are points that the human eye is naturally drawn to (for some weird reason). Generally, putting something of interest on one of these lines (or very near) will make it seem much more significant to the person viewing your screenshot/map. The points where the lines intersect are the strongest focal points - my own commentary on your picture suggests that (The first thing I commented on wasn't the red hall, but the lava-pools in front of your lions, which lie closer to a focal point).

The best thing to do is keep this in mind when you're initially making the map, or to adjust the angle from which you take the screenshot so the point you want the viewer to focus on is the point they do focus on.

Useful Information and Future References

1. Attaching PointLights to Lamps
   

• Create a light (not a lamp), set the colour to black (0, 0, 0)
  
• Copy the light's name (from the first tab)
  
• Click on the light you want it to be attached to
  
• Go to the second tab and paste the light's name into the white box labeled 'connect'
  
• Change the multiplying values (which are initially set to 1.0) to something that suits the situation - for yours, I would suggest something between 0.3~0.5
  
• Check how it looks in the map-viewer (you can't see it in the level editor)
  

2. Making things look pretty

• Colour Theory (simple)
  
• More Colour Theory
  
• Rule of Thirds
  

Hopefully this is helpful - and please, don't take any of this as a personal attack D: I'm just trying to help you improve your mapping skills (and you posted in a criticism thread, so I don't know what else you would be expecting). That said, I'm sorry if any of this seems really harsh or uncalled for - if you think something is an insult, ask me what I meant or to re-word it!

And, on the topic of improving, my first map was a very small room (one wall-length squared) with a wardrobe that had a grunt in it, no door, a rug on the floor, a couple of rats, and no lights. I thought I was the best mapper in the world.