CPU change (lower base frequency, but new architecture, so....?), graphics bump, (much?) better battery life, (large) bump in SSD at the same price point as last year's model. Still under-loaded RAM (4 or expensive 8GB), considering how web apps have exploded in RAM spend in recent years.
Here's one from the Verge's Compare builder: http://www.theverge.com/products/compare/7141/5777
CPU change (lower base frequency, but new architecture, so....?), graphics bump, (much?) better battery life, (large) bump in SSD at the same price point as last year's model. Still under-loaded RAM (4 or expensive 8GB), considering how web apps have exploded in RAM spend in recent years.