I ran a 4.1 system for a while and really missed the centre speaker. Sure it works but as has been mentioned already it really helps with placing the voices into the image.
This series really isn't as good as the previous two. It's also filmed to be very dark, which when the signal is compressed for the TV channel, means a lot of loss of detail. To be honest, I'm not surprised it got cancelled.
I have a dedicated room for my system so I am lucky. It has a tiled floor though so took some taming. I bought Bass Traps from Gik Acoustics for the corners and the back wall, which I don't sit against. They worked really well. Gik offer an advice service and also, I believe, will print pictures...