The first and most obvious thing you will notice is the changes to the user interface.
The number one thing you are going to notice is the toolbar tabs. The Tools (T) pane is now organized in context sensitive tabs. So like minded operations are grouped together, like so:
Personally I am a huge fan of this change, it makes the UI much more streamlined and cuts down on the noise.
There is another UI change that I personally love, as I love very sparse windows when possible. You can now collapse menus down. For example, you can now go from this:
Simply right click, select Headers->Collapse Menu. Again, I like this change.
There are several other UI refinements, but those are the most visible.
First they’ve added the wireframe modifier, which is useful in a very limited number of scenarios. Basically it makes a (3D) wireframe out of the selected model. So this:
NGon tessellation has been improved. No more holes on bad geometry.
In 2.69 it did this:
Now it does this:
Bevel has more options now:
Laplacian modifier added. To be honest, I don’t really get this one yet but it sounds pretty cool.
Of particular use for game exporting, the triangulate modifier has been improved with more fine control over how triangulation will occur:
Game Engine Changes
PSD File support added.
1st person shooter style camera controls (WASD).
Level of Detail (LoD) support added:
Cycles is probably the biggest improvement portion of this release. Probably the biggest new feature is WIP support for volume rendering.
CPU support has been improved, shader language updated to increase performance and a host of other changes.
There were a host of other improvements including threading improvements for the dependency graph, API updates for the NPR (non-photorealistic) renderer, motion tracking improvements, general bug fixes and more.
All told a very nice release, with some great first steps for an improved UI.