Welcome-Emails - Die Geheimwaffe im Email Marketing

I recently signed up for this new start-up called Thumb. Thumb is a site where you can vote on user submitted questions and images with a thumbs up or a thumbs down. (It’s very addictive if you like giving your opinion on things!)

So, I signed up, and immediately after signing up I receive this welcome email, and I liked it so much I wanted to share it with you.

Why is this email so outstanding, above and beyond all the other emails/sign up/welcome/confirmation emails I receive?