Not OP, but the problems I remember are:
Inconsistent use of query parameters. Retrieving metrics for managed Elasticsearch requires more parameters than almost anything else.
Inability to get arbitrary percentiles in the same query as “standard” percentiles.
Documentation is awful. I found it was mostly good enough to get you to raw JSON output, and then it was on you to figure out how things worked.
The delay is a killer. I understand eventual consistency is a thing, but that’s not really useful for metrics. Please, for the love of $DIETY, record them in a fast store and long term store and don’t make me wait 10-15 minutes for ELB metrics.
