THE KNIFE CAN DEFLECT BULLETS. I repeat THE KNIFE CAN DEFLECT BULLETS
Oh yeah, super useful once I figured that out. Means you don't have to be quite as defensive all the time, speeding up the game's pace. I also was able to knife the riot shield enemies to death through their shields on certain occasions, although it was blocked on others. You can also knife the basic gun grunts through their cover. And you can knife while reloading. The knife is a very useful tool.
Only thing I don't like is having to bend down to pick up materials. Wish I could just walk over materials to collect them.
I think that's so you don't accidentally pick up the last material in a collection mission by accident, if you're still looking for other things. On thing I wish they did was let you pick them up during a roll. You do if the item was dropped under a spot that you can only get to by rolling, but not otherwise. If, again, it's to prevent accidentally picking up items, then they could make it so you only pick things up during a roll while holding down. It would increase the pace of the game quite a bit more.