shadows use up more graphics computing power than anything else due to the way DX9 works. there is areason why graphics cards have shaders (that only process shading) built onto them (well all DX9 graphics cards). thats why there are more important things that what its clock rate is, like how many shaders, and pixel pipelines, and stream processors...... (well those are a DX10 thing).
and the new bliz improved graphics engine is not fail. not even a little bit. wow has never, and will never, be a very recource demanding game. a low end system can play wow, with the settings turned down. however, crysis, my computer doesn't even meet the minimum specifications (single core ftl), and my gpu was the minimum reccomended, which means fail.
for what the game looks like, the game is done really well, and is overall a very recource efficient game (its not as good as say half life 2 e1 (when they introduced HDR)) also the number of addons you have have an effect on your framerate.
There is more to life than pew pew you know, like staying out of the fire so you can live to pew pew another day