What you think about adding an 
SSAO Compositor to Iris2? Of couse you could turn it off.
SSAO adds more realistic Shadow-Lithhnting to a scene. The famous german Game 
Crysis uses the the technique 

.
-> 
http://www.iris2.de/index.php/Shadow_listener


pros:
Compared to other ambient occlusion solutions, SSAO has following advantages:
    * Independent from scene complexity.
    * No data pre-processing needed, no loading time and no memory allocations in system memory.
    * Works with dynamic scenes.
    * Works in the same consistent way for every pixel on the screen.
    * No CPU usage – it is executed completely on the GPU.
    * May be easily integrated into any modern graphics pipeline.
cons:
    * Rather local and in many cases view-dependent, as it is dependent on adjacent texel depths which may be generated by any geometry whatsoever.
    * Hard to correctly smooth/blur out the noise without interfering with depth discontinuities, such as object edges (the occlusion should not "bleed" onto objects).
Some more examples from Nvidia:
http://www.nzone.com/object/nzone_ambie ... _home.html