I've been trying to make it work for the past 2 days.
Whenever I add a new Google Form, it doesn't appear in the Google Forms window (http://prntscr.com/iawl12 - it's always empty, no matter how many I create). It just creates the post with the shortcode, which also when checking the page of the post, doesn't show any form, just an error - "Unable to process Google Form short code".
I even tested with the autors test case (http://prntscr.com/iawpi9) from here -http://michaelwalsh.org/wordpress/wordpress-plugins/wpgform/sample-form/, and still got the error message "Unable to process Google Form short code" (http://prntscr.com/iawqfo). I'm not sure if the URL has anything to do with this, as I noticed that when creating the Google From it says that it will be created in /wpgforms/test, but in the output it's created in /test/?lang=ro (http://prntscr.com/iawrx9).
If I use the shortcode that is supposedly deprecated - [gform], it does show the form, but that way I have very little customization options.