ehh… It is pretty easy to use but there's way too much bundled stuff in there, you're always under FreeRTOS, and Wi-Fi support is all proprietary blobs (but that's unfortunately the case with every embedded Wi-Fi chip… unlike Bluetooth LE with has multiple fully FOSS implementations)
I don't know what you mean by "way too much stuff", it's mostly use what you want. It's easy enough to disable any features you don't want with their sdk config stuff
They used to even ship a "No OS" SDK for the 8266, but the demand just wasn't there, FreeRTOS is pretty solid for the core competency of their product after all...