The oddness of the s has to do with the angle of the spine.
Do an horizontal flip on the z to see what i mean!

Interesting effect.
But I think the f and t don't work.
Also, z could be a little less curved.
Not sure about x.

This type looks excellent. I'm a fan of the short curves mixed with tight angles. The only thing that stands out to me is the awkwardness of the "s" as mentioned before, and the "f." I think the terminal that is facing left should face right, so it looks more like a true "f" shape.

Thanks for your comments Pedro, Riccardo & Steven!

I'll take another good look at /s/, /f/, /t/ and /x/ and soon post the caps as well.