Caching and parallelization are my complaints with WebPack. WebPack doesn't cache that well out of the box, and plugins like HardSource seem to have errors often enough that they're kind of annoying. WebPack also doesn't have parallelization built in, so you need something like HappyPack. Maybe I was doing something stupid, but I wasn't able to get HappyPack and HardSource to work together nicely.