The biggest overall change comes in the psychic phase. There has been quite a lot of hype about it. Summoning tons of models, invisibility and other crazy powers have taken the internet by storm. For me, I find the psychic phase a nice balancing factor. It finally gives some real interplay between opponents and it adds a nice resource management element as well. It also makes both my daemon and grey knight armies quite happy to throw 12+ dice on the table.
With some other minor improvements , the game has not changed much. There is still some discussion at the LGS about unbound and it's place. I feel that unbound should be for casual games only. We shall see how things go.
Overall, 7th has me excited for my grey knights to rule the table with ALL the psychic dice :D