1. Is there something interesting/novel/intriguing? Something has to capture my interest and show significant value. I mostly write in Clojure, so the bar is set pretty high for this one. New syntax doesn't impress me, building large reliable systems does.

2. Is it elegant? In the general sense: things that are elegant are often also good designs.

3. Do people use it? This is a hard one, and stems from 25+ years of experience. No matter how beautiful or impressive the new technology is, there will be problems, and I am too old to iron them out myself. I've got things to do. So, tough as it may sound, these days I will not start using things that have not seen reasonable adoption. This does not mean I won't read about them, just not use them. And my criteria for "reasonable adoption" are not "everybody and their dog uses it", I just need to see a user base. Also, the threshold is higher for databases. Practical examples: Clojure and ClojureScript are fine, Datomic is not. RethinkDB just fell below the threshold and I have to migrate; FoundationDB is barely getting to the threshold.

Taking Elixir as an example, it fulfills all three criteria. I know what it is, I've seen it in action, I read about it and I keep in the back of my mind as a tool I might want to use when needed.