• The number of JARs seems to have exploded. I can't figure out which transitive dependencies I need and don't need, since there's a lot of "batteries included" by default.

In a regular use case you don't have to remove any transitive dependency, we take a lot of things under consideration when including them by default. Also, removing dependencies can cause runtime errors when not made carefully, so we recommend against it. When you look for dependencies you don't need, what is the main concern behind it?

• The class names are all slightly different, rearranged to presumably prioritize internal consistency over downstream impact (BasicAWSCredentials -> AwsBasicCredentials, AWSStaticCredentialsProvider -> StaticCredentialsProvider, etc).
• Once you do find the correct class, you inevitably must perform either the "constructor -> builder" dance or the "constructor -> factory method" dance.

We understand that a lot of manual work can go into the migration. To assist with the code migration we released a Migration Tool that uses OpenRewrite to automate the refactoring from 1.x code to 2.x code. It is currently under preview release, and transformation of some clients are not supported yet (like AmazonS3Client, TransferManager and DynamoDB Mapper). There's more information in the Developer Tools Blog Post and in the Developer Guide, including steps to execute the tool and a list of current limitations. We encourage you to try it out, all feedback is welcome.