Two brief comments: y has some issues, l seems less slanted than j.

Better? Also, how's the z? Anything else I can improve?

I'm by no means qualified, so mind the salt ;-)
The left stroke of y appears too rigid compared to the rest of the letter(s).
Upper loop of d doesn't flow well.
Bottom of t is dark.
Hook of j has something that I'm unable to pinpoint.
! is a little too lively compared to other glyphs.
z is a little light.

How's this? I've redone the bowls of the a and d entirely. Flow better? I corrected the other issues too. Any thoughts? Other letters also need more help?

I love it! Brian
Congrats for this great family.
And Bonus points for making it available for free in the Google Web Fonts Library.

The new a counter is much better.

Here's updated italics, I'll be posting a PDF later. The additional italic I'm calling "cursive", because of the cursive structure of the letters, not because it's connected (it isn't), although I'm wondering if making ligatures of some of the letter pairs wont improve the word image. Or maybe make special contextual alternates that connect because of their structure, like a running script would.

The main italic is pretty much a "slanted", although the lc is completely redrawn. And, I changed the serif shapes a bit.

Italic:

That Cursive is brilliant! Following the tradition from the Renaissance on, I would like to see the Caps more upright in the Cursive.

Cursive:
/vw ce/ could be slanted a bit more.
/s/ is top heavy, which is not necesarily bad, but it could also be a bit more slanted. (Note, slanted doesn't mean 'more like the italic'.)
/o/ seems to be upright, because of the white space inside. I had the same problem with my own italics. It just needs to be slanted further, focusing on the whitespace.
/zero lining/ has same problem as /o/.
/one lining/ the two strokes are disconnected by the swashy ink trap.
/z/ is a bit too computarized and not enough calligraphic. Look at the italic /z/ in garamond and jenson and such.

Italic: Looks silly next to that wonderful cursive. No specific issues, just a lack of cursiveness. I don't like that /x/ but that might be just me.

Cheers! jasper

In the cursive, ! looks a bit upright and/or too tightly spaced.

That cursive is nice. I think it could benefit from looser spacing though. In 2, 4 and 7, I would try to get some curviness into the horizontals. Look to your z for guidance. I agree with jasper re o and s. y and g are nice and quirky. I'd make the exclamation mark curve away from the sentence rather than into it - i.e. Unslant it, reflect it and reslant it.

What I was saying about exclamation - just use the one from de stijl sample above