Gradle is really powerful if you know what you're doing and you take the time and effort to keep your build optimized, sane, and working. I recently built a Gradle plug-in that allows us to build native components on a remote system (z/OS) and integrate these tasks and artifacts with the native Gradle model so that Gradle takes care of caching and parallel task execution. I'm sure this is possible with other build tools as well, though, but the Gradle model fit our use case nicely.

I think any complicated build system will eventually devolve regardless of the build tool if it's not properly maintained; the variability of the required tasks is just too high.

Gradle does seem to be moving fast with regards to Java support in general changes and improvements in the build tool. It takes effort to keep up, but it's worthwhile.