ok im opening pandoras box here.(treatment vs framed wall art)

Glass is very bad it will kill your sound.

oleschool:

My listening room - living room has glass windows behind the speakers and along one long wall. So it is a challenge to improve using the old standard acoustic treatment technology. 

I now have a fabulous listening environment using the Synergistic Research room treatment products. They have bullet sized transducers of three varieties that allow you to tune a room. HFT, HFT-2.0, and HRT-X.
These are small and not visually distracting.

I think the Synergistic Research products due the best job of treating rooms. If possible go to the Rocky Mountain Audio Show (Denver) in October to hear and talk to them. They also have good Face Book demonstrations and how to suggestions. 

They are sold with a 30 day return policy so well worth a try.

David Pritchard

Unfortunately glass will have to go. Notwithstanding the suggestion to add SR products these will only tame but not remove the effects of the highly acoustically reflective pictures (I have a full SR ART and HFT setup originally installed in my SoCa all glass modern house which you can see in my old system description)

 I experienced just this in my new room gradually eliminating each piece of artwork and hearing the improvement at each step. I still have a window but that is itself heavily treated. There's no comparison in how good the two rooms sound

luckily manufacturers of acoustic treatments have realized that not all of us want to look at plain cloth so are now making acoustic panels that double as art, for example ArtPanels from GIK acoustics are well priced and attractive. 

+1 for GIK Acoustics.

Also, sculpture can act as diffusors. :)

If possible, remove the glass or replace with museum quality plexiglass which maintains UV protection but is less rigid, and not as good a reflector. Also, use foam behind the frames to prevent rattling from the drywall.

Avoid reflectors most of all at 1st reflection points.  However, you can compensate for too much glass somewhat with lots of diffusors and dampening elsewhere. For instance, the ceiling is often overlooked. :) 

Best,

Erik