Since I review maps, I look for a few things in a map. The first being of which is the setting or theme of the map. Settings like TFCs' Avanti or Frontlines' Lombardi, which I am aware are basically the same, are my favorites because of the textures used to accomplish the Italian-like atmosphere. Eye candy is also very important. If your going to be sniped, you should at least have something nice to look at while you wait to spawn or the round ends.
Lighting is extremely important in most mods.
With the realism found in CS, you can't afford to be in a totally dark room with who knows what. Most mods have player classes that blend in well with some backgrounds and if the map is dark then that makes it all the worse. Basically the main aspect I feel maps should focus on is visuality. Sometimes the gameplay can suck but the ambience and look of the map can make it one of your favs. Visuals are nice in my book, as long as they don't distract too much.