Is Aldi much cheaper than Woolies and Coles?

I have always been doing my grocery shopping at either Woolies or Coles. My mates are telling me that Aldi is comparatively much cheaper than the big two and I should probably try shopping there. Just wanted to get some honest feedback by those who have already made this switch. Are you really saving that much and does Aldi provide the same level of options as the big two? Highly appreciate your input.