X2 is a huge update but in contrast to X1 we focused on workflow enhancements and major improvements to the fundamentals and backbone of the program, addressing hundreds of longstanding requests and problems. The big top level areas are Automation lanes, editing and rendering improvements, take lanes, editing tools, zoom, snap, Pro channel updates, PC FX Chains, Matrix and realtime preview, UI updates, performance improvements and bug fixes. All these are areas that intersect with at some level with every SONAR user.
I'll put together a more detailed list of all the areas touched from our internal notes once I catch my breath, but for now watch all the videos being put out since they will give you a good idea of the breadth of features.