I found this most helpful, and haven't seen him explain it this well before and didn't want it to get lost in the comments of node/3184 'Why's there fewer starred submissions these days?', so I politely quote it here.
eihrul | 2011-10-15 01:40
The problem is that the mapping community is shooting itself in the foot. Quadropolis built mappers from the ground up, but now tries to operate at a level of sophistication that does not allow mappers to get feedback and grow. As has been said, new mappers are shoved away when they want community and feedback. Its standards are too high and simultaneously the wrong standards. I have a rough set of standards which I apply to maps for inclusion, which are really a balance of many aspects. If you only focus on one of the aspects, to the neglect of another one, the map is unlikely to get included. If you do a passable attempt at all of them, the map is likely to get included, even if it is not amazing. The bar is not amazing, the bar is balance. They are:
1) Performance. If the map is 400K verts because you spammed lots of little details everywhere, it is probably not getting included. 200K is more or less a sane top-end for big Hallo-sized maps. Spamming lots of water planes is almost always a no-no, especially in combination with spamming lots of geometry, since they multipled eachother. Try to stick to at most 1 water-plane in view at any one time.
2) Texturing. Texturing matters not just for appearance, but so the player can actually see where the hell they are going. I'm not trying to single anyone out, but if I am handed a map with very complex flow, and all hallways look the same because it's one solid gray mass or a such a noisy mass of random textures that I can't remember a pattern to them as I am running by, then the flow of the map has become more theoretical than actual. And, well, neither looks nice either. I may as well be running through a dark and twisty maze only to be eaten by a grue. :)
3) Lighting. The comments for texturing above apply to lighting, though with some slight difference. Too much noisy lighting with lots of different technicolor lights or almost-moire-pattern shadows from competing lights can make it hard to see and it just looks ugly. Even a simple sunlight with some skylight with some occasional accent lighting can be good enough for a lot of maps. Most people just try too hard here.
3) Geometry. I am actually rather forgiving of blocky detail, and people tend to overfocus on geometric detail to a fault. Spamming lots of noisy detail really tends to make maps look worse in general, and actually detracts from nice texturing and lighting, especially the texturing. You need to work with the cubes, not against them. Large details tend to work better than small ones, especially because at the pace people run around in Sauer your small detailing will mostly be ignored as people run by like cheetahs. Let the textures do the small detail.
4) Particles. Don't spam them. Sometimes particle spam can work in the right context, but usually it just looks a bit lame. It's not a deal breaker, but never the less, lame.
5) Mapmodels. Same caveats as spamming lots of small geometry detail.
6) Flow. Cramped tunnel systems or cramped hallways are bad. Too much verticality is bad. Too many teleports is bad. Too many jumppads are bad. Too open is bad (especially in CTF and capture), less so for FFA. Too many twists and turns is bad. The most popular FFA layout in Sauer seems to remain a hole with a ledge around it (complex). I think people overthink this one a lot as well.
7) Items. I think common sense mostly reins here, and that it is rare for people to really screw this up badly. Make sure items are available at appropriate frequencies according to their benefits. It is perfectly okay to omit the quad and health boosts and yellow armour in a map if you don't like their effect on gameplay for your map too, but generally all other items should be present. Quads/health boost/yellow armour very rare. Green armour kinda rare. Rockets/chaingun should be used judiciously. Shotgun/rifle/grenades a bit more available than rockets/chaingun. Health to taste. Pistol cartridges should only be placed only to insult/spite the player, but are not terribly useful.
8) Clipping. Usually I end up going in and fixing this myself on almost all included maps, but people never clip their maps adequately, so that the poor baby kittens escape and fall off the map and die. Save the kittens.
9) File size. The Sauerbraten download size is already big. Many people still have shit connections, and even if they don't, a huge download makes it less likely for impulse downloaders to try out the game because it will still take a long time to download. I don't care if you think otherwise. The download is not increasing 20MB for an FFA map, and even 5MB will make me skeptical. For 5MB, your map must be pure unadulterated awesome-sauce, like, better than almost every other map in the game. Smaller file size maps that are less a hindrance on the total package size are more likely to be included.