It supposedly is much nicer to configure, and is better at stripping out unused code (so it would lead to a smaller JS bundle). Of course, Webpack 1 is working out fine so far, so let's wait with upgrading until all the major issues that will be discovered upon release are ironed out.
Webpack 2 is about to be released in a few weeks:
https://medium.com/webpack/webpack-2-2-the-release-candidate-2e614d05d75f#.p217rv6sk
It supposedly is much nicer to configure, and is better at stripping out unused code (so it would lead to a smaller JS bundle). Of course, Webpack 1 is working out fine so far, so let's wait with upgrading until all the major issues that will be discovered upon release are ironed out.