I just wasted a whole afternoon on this module. The module now requires that the api class be installed separately. This is not documented on the project page and none of the other documentation is updated. Only the release notes mention this and you don't see those when you are installing with drush.
Finally I found a mention of the make file and I tried to run it but it created the libraries folder in the module folder as there wasn't good documentation on how to use the included make command.
Then I moved the php class to the "sites/all/libraries/mailchimp" folder and on the reports screen of the site I still see an error message that the mail chimp class cannot be found.
MailChimp Not installed
You are missing MailChimp PHP wrapper class required to use the MailChimp module. Please download and install as a library.
I am sure it is in the right spot in the libraries folder and I have tried clearing my cache and disabling and enabling the mail chimp and libraries module and I cannot get this module to work for the first time.
When you take a library out of a module please put it in big bold red letters on the module page.