This suggestion is just based off my personal opinion and you might think otherwise but, nonetheless, please take your time and read through my simple suggestion. Also it only concerns visual effects and nothing else (damage, cooldown etc.).
According to me Gandalf the Corrupted's Dark Word of Power, visually, couldn't live up to Word of Power or Bright Word of Power. I mean the latter two seems like these awesome power blasts emmiting all around Gandalf and, not only does it deal a considerable amount of damage, but also looks unbelievably cool.
Now the first time I got Gandalf the Corrupted and saw his level 10 power I had the highest expectations for Dark Word of Power, being a fan of evil myself. I mean the dyscription alone has enough mojo to send shrivels down my spine.
Most unfortanely when I activated Dark Word of Power the following happened:
1) These weird, black, branch thingies started twitching around Gandalf ceating the illusion that my screen was spazzing out.
2) The black things dissappeared and a very faint wind seemed to explodd around the Ring Hero.
Now I, for one, am a person who pays immense detail to graphics. This is what got me hooked to Edain in the first place. And, although, Dark Word of Power doesn't look like bfme 2 visuals and is actually not a bad animation at all, I still expected a bit more.
Now here's where my suggestion comes in
A really cool massive area of effect power was the Witch-King's Halo of Angmar. Now, seeing as it was removed from 4.0, I thought that effect would fit Dark Word of Power like a glove!
Just change its colour to a more red-and-black scheme, maybe add a small delay before the burst (like Word of Power and Bright Word of Power) and viola! The perfect looking Dark Word of Power!