I had an ATC-600 GX1 for a little while. I had high hopes for it because of the fact that it took a full ATX power supply, had space for a couple of optical drives and a couple of hard drives, and allowed full-height cards.
The problem? It didn't live up to its promise, at least not for me. First, the case is (to me) a complete PITA to work in. Just about anything you do means that you have to remove the 6 tiny screws holding on the top reinforcing bar (which, by the way, blocked most of the airflow for my NV7M/PAL 8045/L1A setup). The drives were just as difficult to install and work with. Cooling was pathetic, stock is 3 60mm fans. To me, 60mm fans are a waste; to get any of them quiet enough to be bearable means that they no longer move enough air to be worthwhile. Airflow for the 60mm fans on either side of the case were impeded on the one side by the stamped "grill" in the case, and on the other they were less than an inch from the side of the drives. And not in a good way, they were basically useless. The rear 60mm did a great job of moving air away from the back side of my video card, but not much else. It was too far from my northbridge or CPU to include either of them in the airflow. I ended up cutting another 60mm hole in the rear panel (nerve-wracking on a brand new $220 case with very little room for error) right next to the stock hole, and that helped a bit. A very little bit, like 2C CPU temps. As you can tell, it just wasn't the right case for me.
However, if you have a decent budget and are content with the lower power CPU's like the C3 or Tualatin, it might make a decent HTPC system. If I had a decent budget, I would use this case with an Epia M 6000, 3 VERY quiet 60mm fans, a Nexus PS (or even one of those fanless ones), a single Barracuda V mounted in a silent drive enclosure, and a very quiet optical drive and that's about it, and I would also lock it up so that I wouldn't be tempted to get inside the case and tinker about...because that reinforcing bar really used to piss me off.