How can I quickly and effectively debug CloudFormation templates?

Use the aws cloudformation validate-template command in the AWS CLI tool. It only validates whether your template is valid JSON or YAML, not whether your keys and values are correct (for example doesn't check for typos in keys)

Another option, a year later, is to abstract these templates to a 3rd party library, such as troposphere. That library constructs the JSON payload for you, and does a lot of validation along the way. This also solves the "Wow managing a 1000-line JSON file sure is sad" problem.