Okay, so I finally had the chance to go see what the fuss with the new Shadow thing was today! My assessment of them is: Shadows are way too bloody dangerous now in comparison to Shadow Fiends. Let me elaborate.
I took my level 12 moron out to see these things as he has a hefty 29 AC when unbuffed and a Fortitude save vs. Negative Energy high enough that he physically could not fail the saves so he could plow through the place with laughable ease. My first run through the place was on a moderate spawn (entirely Shadow Fiends) and I cut through them without taking more than 20 damage from the entirety of the forest. I reaped my rewards, rested, full healed off it and left; No problem.
My second run was significantly more painful. The very first encounter of Shadows (two of them) actually crippled the character and I couldn't move on. In the time it took me to cut these two down (which was extremely quick since I hit with every attack and had Power Attack mode on), I had taken 4 Strength damage, got Heavily Encumbered (cursed heavy pack) and Completely Exhausted. I checked the battle log and it seemed like the Shadows were over-coming virtually every point of AC I had as they hit me on total rolls of 13 and 14, less than half of my normal AC and my character is a Dex-Rogue. I believe his rough Touch AC (by 3.5 rules) is around a 19-20.
Obviously, this was without a NE Protection potion/spell, but still, that's a little... Excessive. Especially for a CR3. Now, I don't have much of a problem with them as is, but if they're going to be this difficult, I'd suggest putting their CR up to a 4 or a 5 to reflect the actual party needed to handle it.
Also, the fact that a CR3 Shadow is more difficult than a CR7 one is just wrong in my book.
My two cents.