Since version 1.23 b33 (as far as I can remember), ZDoom is capable of bridge-things (inspired by Hexen and the K2-Bridge developer Kurt Kesler) and since then, doomers often use this feature to enhance their realism and feel for real 3D. Well, but often, being able to do a bridge in ZDoom doesn't mean, that it automatically contributes to the realism and 3D-feeling.
Think about bridges which are far to long, almost floating in the air without any pillars or chains to hold them. Think about by far to simple floor patterns for the bridges or about missing rails.

Well, with the help of shot 1 I will try to explain the standards of bridge-design for a realistic result in ZDoom. First at all, don't always use the standard-bridge pattern of simple squares being connected to each other but rather vary the forms and shapes. In my example bridge, I used diamond shapes to build the floor, ut you could also use triangles, pentagons or even abstract forms. Another important thing is the length: Don't make your bridge-parts longer then 192 units without adding some pillars or chains to hold their weight. Just think on real bridges, their leverage and the way they were built. And at the end, add rails to your bridge (with the help of some ZDoom tricks, you can make them passable (jump) for the real 3D illusion). The example shot demonstrates all this very well as I think. (buildtime 20-25 minutes)

Summary: Bridge is not bridge! Many small details - floorpattern, rails, physics - added to your fake-3D-object make up for a real good illusion, a real good K2-Bridge. Without these details, your map heavily losts its authenticity, so work hard on them if you want to have bridges!
Extra-Buildtime: "20-25 minutes" (depends on size and complexity)
Build-Difficulty: "Med - High"