First of all, don't give up.
As a new grad, you'd feel overwhelmed no matter where you were. Second, don't expect to learn it all at once. Ask questions!! Also, set aside some time at home to study up on the things you've seen at work. I know, sometimes one of the last things you want to do is crack a book after work, but do it right away, while it's still fresh -- don't spend a long time reading, just enough to debrief yourself. Find your support people, as Gary mentioned.
At my hospital, we have a year-long orientation for new grads moving into critical care, and we only accept those who have had certain experiences prior (EMTs, LPNs, etc.). The new grads I've dealt with through this program have all done quite well. In general, though, I think that they should have some floor experience first -- not a lot, necessarily, maybe only six months or a year. That amount of time will allow one to learn their organization skills and get a handle on the basic assessments which are expanded upon in critical care.
However, with the nursing shortage getting worse, I think we'll be seeing more new grads in the ICU and ED settings, so we all have to remember to help and teach.