I'm *REALLY* happy to see the long lost of bug fixes. I am currently focusing on mobile which is why 4.2.2 was disappointing; it was supposed to be a bug fix release but it didn't actually fix many bugs. So far it looks like all the big known bug issues are better, including the really annoying flickering shadows.
Performance is much better on complex scenes. They had been talking up their new culling system and mobile device processing improvements for months, and the work certainly shows on the hardware. Good job Unity Devs.
I like how they didn't break everything when adding 2D. All the new 2D support is nice and I'm sure many pixel artists are thrilled at the prospect of new jobs, but right now most games using the engine are 3D. The ever-present 2D button on the Scene view is mildly annoying since I'm working on 3D stuff, but understandable because this is a first pass and it was bound to have some mild annoyances. I was a little worried that existing features would suddenly turn 2D-centric. So far there are just some menu items and that one ever-present 2D button that I don't see how to turn off.
The new MonoDevelop 4 is WAY better than the old MonoDevelop 2. Not enough to make me give up UnityVS (the tool that integrates Visual Studio with Unity) but it is enough that the tool looks usable. I am guessing that when I need to use MonoDevelop, it likely won't feel quite as painful.
Morph targets are something animators are certainly cheering about, but for a programmer not so much. They can now target their morphs... or something. For my hobby projects regular skeletal animation is good enough.
I can tell there were some incremental visual changes that were made, but nothing that I really notice. I hate it when companies randomly decide to rip out great features or dramatically change the look with no option to keep the old styles. This still feels and acts basically the same.
Other than that it still looks like unity, which is a good thing.