is your resolution set high enough? Anything under 150dpi will look blocky (300dpi usually does the trick).
And what do you mean with "way too big in adobe reader" - is the page size off? You can check the actual page size under File>Properties…
Or does it just show a part of the page when you open the file.
I don't think there is an option in Photoshop to make PDF files display as "fit to window" by default.