Many things that ES2015 provides are nice of course and the code looks a bit cleaner, but apart from a few real innovations most changes seem to be syntactic sugar.
Also, I found that each step in my build chain made it more complicated to build and maintain my code, especially for other developers. I eventually even abandoned Gulp (which in my opinion tries to reinvent Unix pipes but does it all wrong) in favor of a simple Makefile that chains a few build commands and uses inotifywait to watch the filesystem for changes in order to automatically rebuild the code during development.
Another thing I do which may shock many JS people is to actually check in the build directory of my setup into version control, because this makes deployment much easier and ensures that I will always have a working version of the code in the repository, even if some external dependencies should change in the future. This also eliminates installing extensive tooling on my production servers, which itself is a large burden and creates many security issues (for a simple setup consisting of rabel, react, require.js and a few support libraries, node.js downloads about 350 MB of source files onto the machine).