Below is screenhots comparison for shadows on "ULTRA" on 13.12 vs 12.2 live.

Same place, same gamesave and in-game time, but fps is 30 vs 60 (literally!).

New shadows on "Ultra" seem to be infocused (notice they has less brighter "outlines" around them). This new shadowing algorithm seems to cause massive fps drops (and really blurry outlines for shadows).

So, ultra shadows, 12.2 live (60 fps) vs 13.12 (30 fps) below (performance stats included now):

http://www.framecompare.com/screenshotcomparison/FECF1NNU

Old comparison (without fps and stuff):

http://www.framecompare.com/screenshotcomparison/FE22CNNU

Shadows on "High" are noticeably more blurry on 13.12 vs 12.2 as well, but at least they don't seem to tank the performance (I got 60 fps for both 12.2 and 13.12)

http://www.framecompare.com/screenshotcomparison/KGPZLNNX

Devs, please fix this! We want shadows like they are in 12.2 (both look and performance wise).

P.S.: Temporary solution for those playing on 13.12 - set your shadows to "High" for now to get decent fps.

@Ada Good detective work there. Yes, devs should revert the shadows. The new ones look worse. It's a really bad combination when things get uglier and you get less fps on top of that.

@Ada
The Ultra shadows look particularly "work in progress", what with the strange clipping around the blur effect. Let's hope this is just something they haven't finished yet, and we'll get a final, well-tuned version on release.
Soft shadows are nice for sunlight through trees, but certainly not a tradeoff worth sacrificing this much performance over.

Nice bit of detective work, thank you!