Dang it... I bought an Antec 300 a few weeks ago to finally replace my old case circa 2003, and then the new Antec 300 is released! 🙁
I don't quite like the idea of a toolless case though - things aren't as secure in it, and I already use a screwdriver to remove the thumbscrews on my case (I want to make sure they're completely tight and won't vibrate or anything). I really don't mind needing a screwdriver to secure things, and would actually prefer it. Also, having the PSU fan on top isn't too bad - mine's mounted that way because otherwise there's almost no airflow for it, and all works just fine. I've got a Coolermaster hyper tx3 cpu cooler (92mm fan), 2 HDs, a seasonic s12ii (regular height), full atx motherboard, and a evga geforce 550ti (9.5" I think), and it all fits pretty well.
All in all, this Antec One case isn't bad, though I don't get what the bulge on the side is for. I'd like to see them make a small micro-atx or mini-itx case though, like a business SFF machine, using a smaller psu and all (Not ISK-150 small though - the airflow is too limited in there unless you're running an E350 or 2100T, and I've heard of i3 2100s hitting 80C under load in there). For people like me, who want dedicated graphics cards and lots of upgrade room, a mid-tower case is great. However, for someone who just wants to surf the web and is fine with an i3 and integrated graphics or an AMD APU, great airflow and lots of upgrade room, including the ability to have a dedicated gpu, just isn't needed. Something smaller would work just fine. I haven't seen any good options there, most being from companies I've never heard of.