A bit disappointed with the gaming performance so far (seems like 1/2 games are that much better than a 2700x [FC5]) and they don't seem to clock too well (TPU had the 3900x at 4GHz, granted they had issues with cooling; G3D hit ~4.4GHz on the 3700x, which doesn't bode well for the rest of the line up).
A stock 1800x seems to be about 11% worse than a stock 3700x at 1080p, which really doesn't seem much of a step up considering the clock-speed differences. I'd assume the boost-clock-bins are similar that if the 3700x hits 4.2 @ ~16 threads used, the 1800x would hit ~3.8 [based on what the 3900x does].
On the other hand, 12 cores for $500 and 16 cores for $750(?) seem like a great value especially if upgrading from a 1xxx or 2xxx series CPU.