The Corsair Obsidian 800D looks cool, but the CM ATCS 840 destroys it as a whole. Why? Well, the ATCS 840 is cheaper, it's made of very thick aluminum all around (save the side panels), it has better water cooling potential (by default, you can use a 360 rad and a 240 rad inside), better airflow, and a removable motherboard tray. Hell, I'd take the HAF 932 over the 800D. Better airflow and water cooling potential, for $130 less. I can't see a way to use a 360 rad on the bottom of the Obsidian 800D. You won't be using any rad down there by default.

If the price on the Obsidian 800D was $180 max, it might be worth looking at. But $280 for an almost all steel case that has worse airflow/water cooling potential compared to several much cheaper cases seems silly to me. Of course, people will buy it since it has Corsair's name on it.