Okay, so for the most part they are good things. I can usually bounce off them to help me get to where I want to go. The best thing about walls is that it's so much easier to just let them stop you, instead of having to expend all that energy to stop yourself. When you run at them, they don't move and stop you dead in your tracks. It's awesome! Much more stable of a stopping device than M-Guy's legs.
The one downside is that I think they are built similar to the stairs in some way. Much like how the stairs move out from underneath me right as I put my feet down, the end of the walls called "corners" are not so stationary. It seems to happen most when I turn around, but the corners randomly shoot out and extend themselves to make openings smaller than the first time I passed by. Not a huge deal until you turn around right as they shoot out into your face. Man does that sting. So my lesson for today when it comes to walls - Aim for the center!