I take it you're talking about map design, because charcters usually are not lightmapped.
realism for realtime rendering is pretty hard to achieve.
Global illumination may give you some realism, surely more than simple lightmapping. Of course you need to know what you are doing with the settings of the lights and the illumination renderer (eg. gile[s])
I also think you need a high polycount for realism, but that is exactly the thing you should prevent in realtime rendering like in games. So maybe the Polycount is the part of realism you need to sacrifice for the sake of speed.
Textures need to be good. In my opinion nothings wrong with using photografs, if you use them in a clever way.
Some things are important for the screen design: all textures need to use a color saturation that is within a certain range. I call this step "saturation equalisation": simply load all textures in your graphics app, display them as thumbnails and adjust the saturation as well as the brightness/contrast to make sure all textures will fit together nicely, concerning color saturation and brightness/contrast.
Antialiasing is also vital for realism. But this may be added by the user, if his graphics card offers this feature and is powerful enough.
Here's an image rendered by Radiance, one of the global illumination standard apps:
Of course not made for realtime. But I think Blitz could render a gile[s]-lightmapped mesh like this one easily in Realtime.
It may be a lot harder to get good looking vegetation like trees and grass etc. If you are investigating the oblivion vegetation system you'll notice they use a lot of tricks to give the impression of high details but they actually use lowpoly models. It's an art discipline by its own to produce good looking low poly trees and grass etc.
