When it comes time to detail a Team Fortress 2 level, the path most mappers take is one of trying to make everything look visually stunning, no matter how important or unimportant the area in question is. Even if detail is planned out beforehand, the initial reaction seems to be to make sure everything is a point of visual interest. Unfortunately, this is not the proper way to handle detailing: in TF2, gameplay and visual elements are closely tied together, and their relationship must be considered when detailing, because your points of visual interest are what the player should interpret as points of interest to the level’s gameplay...

Read on Nodraw.net!
http://www.nodraw.net/2010/08/tf2-density-of-detailing/

Do you ever feel that your Team Fortress 2 map is just missing something? It plays decently, it is enjoyable, but it is lacking something that really puts it over the top? Here are some common features in Valve maps that are often missed by community mappers.

Height Variation
If there is a single most important factor in determining whether your map is fun and interesting to play, or plain and boring, it is height variation. Changes it height make the map much more entertaining, offers strategic options for various classes, and quickly makes the map layout much more intriguing to a player. Height variation can also serve a function purpose, such as funneling spam, breaking sight lines, or improving optimization...

Read more: http://www.nodraw.net/2010/06/tf2-what-your-map-is-missing/