I've had a lot of fun using Espruino on the ESP8266 platform for various sensor applications. The biggest hurdle was keeping things simple. It's easy to get creative with JavaScript resulting in memory overflows and hard to debug issues. I eventually switched to Node.js on the Raspberry PI as my use case did not require low power / small form factor.

Playing with the bangle.js espruino watch has been great fun. Nice hardware (much nicer than the esp32 based lilygo), and there's a coolness factor in programming your own watch to work exactly as you please.