Every time I read about some new solution to storing time series data, I always feel like I must be doing something wrong, but I've run into _zero_ problems yet.

Every time I have to store time series data, I never really need ACID transactions. I definitely don't ever need to do updates or upserts. It's always write-once-read-many. ElasticSearch has always been the obvious choice to me and it has worked extremely well. Information retrieval is incredibly robust and for times that I'm worried about consistency, I use Postgres's JSON capabilities and write first to there. You can have your application sanity-check between the two if you're worried about ElasticSearch not receiving/losing data.

I find it really hard to beat.