Game environments should always be interesting no matter how ordinary the setting. Even the most mundane of places can be made more interesting with some unusual elements. Techniques I use are things like breaking up uniform outlines (for example, roofs, fences or walls), with other objects to keep the scene unpredictable for players eye; non-uniform shapes are more pleasing to the brain.
Light can be used to dramatise a scene. Pick out strong shadows and highlights to prevent the scene looking flat and define the shapes of the main structures so it’s dimensions are obvious at a glance. Use slightly exaggerated colour saturation to avoid blandness. Having textures with an obvious light direction (for static objects) and matching them to the lighting direction of the game lights makes the scene look far more detailed than it actually is (unless normal mapping is being used).
I like to include features in an environment which give the objects a sense of mass. Things leaning or resting on other things and their influence on them, maybe causing them to sag or lean. Rope, chains or material draped over solid objects. Solid objects leaning on flexible objects such wood against a mesh fence. Movement is also important. Use animating flags, swinging ropes or chains, smoke rising from chimneys, etc; to bringing a scene to life.
A game environment must usually have ‘lived in’ feel to make it believable. Not just by people but anything alive in the environment, plant growth specifically around objects can give the scene a cohesive feel rather than a series of objects that have just been placed together and don’t seem to interact with each other. Each object should look like it has a history, a story to tell. Why is it there? Why is it dislodged? broken? open? closed? etc.