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/