I was getting the same emails and was continually hitting the unsubscribe button, but I figured out the problem. I was subscribed to a number of their newsletters.
Click unsubscribe in any Eventful email and a new page will open. It should say something like "unsubscribe successful", but you're not done there.
Click "take me to email preferences" and you'll see that you've been automatically opted in to a lot of newsletters. Page down to the bottom and click "Unsubscribe from all email" and click confirm.
I hope that does the trick! It's annoying getting all those emails!