Thankfully they patched the difficulty a while back, so normal/hard is actually a challenge. I went back to try out hard mode and found myself getting blown to pieces by some clever trickery on the part of the enemies. Basically while I was running from one grenade, they were throwing another one to where I was heading. Even with slow-mo, the game is actually challenging on hard.
The main thing FEAR 2's A.I. was that it was only smart if you allowed it that precious second to get into position. With the release game, this just wasn't possible, because slow-mo made you unstoppable. Now the A.I. is challenging, although I still think they aren't up to extreme on the original FEAR.
I'm looking forward to this DLC, but I still wish Monolith had spent some time making the guns sound less muffled, creating a MP system that actually worked, and trying to actually be scary. FEAR 2 is just another FPS really, the horror element seems almost tame now.