Although since mid-2018 I haven't touched much AWS except for personal projects (and just a few services), I had the AWS Certified Developer - Associate 2018 purchased and forgotten, so as a way to refresh some of the services and learn new ones I took it during the past weeks.
Note: I confess I either skipped or quickly went through most of the labs as I have already done the AWS Certified Solutions Architect - Associate course and many are very similar. There are some differences like an in-depth multi-video section about Elastic Beanstalk.
I learned about a few services, like X-Ray (tracing and some metrics, like a lightweight DataDog), Step Functions (Lambda "ui"), about the fact that API Gateway supports importing and updating API definitions from Swagger definition files, DynamoDB Accellorator and DynamoDB Streams (too bad events data is only kept for 24h). SQS FIFO queues (new from 2018) also sound cool as they guarantee order and exactly-once processing, too bad they are restricted to 300 transactions per second; still really great to have such power in an easy to use service. More interesting topics were an intro to CI/CD using AWS services (CodeCommit, CodeBuild, CodeDeploy and CodePipeline), how to build Docker containers with CodeBuild and ECR, Cognito and Identity Access Management (IAM) services.
As usual you probably won't use all of them but the amount of pieces you have available as services is incredible, if you don't care about vendor/cloud lock-in, you can perfectly build your whole business on AWS probably for years to come until you might need something more "powerful".
The quiz questions good to practice, as many depict real world-like scenarios and ask you the best service or proper configuration to solve a problem or match existing (but non-AWS) requirements, but I found some of the questions quite bad, as they are as dumb as asking you the exact name of an API method call, or some numbers which might get asked in the certification exam, but also change as Amazon softens some limitations.
Overall, a great and interesting course, with more than 25 hours of videos, exercises, labs, exam tips, and fresh & updated content whenever something new appears. I still recommend going first for the Solutions Architect Associate one if you want breath-first services knowledge, but I enjoyed both.