One thing that is nice is that if you have a six core machine you now get six parallel kernels!
I don't know if I like the Predictive Interface very well. As many people know, I like to view the notebook interface as a plain piece of paper that I write on. With the New CellInsertionPointCell, and now the Predictive Interface it is gradually morphing into something that looks more like a palette. How many more doo-dads are they going to add? And the little buttons tend to interfere with other material on the page. Many will like these features, but if you don't like them you can disable them. The CellInsertionPointCell feature can be disable by an option for the notebook (in the Style Sheet say) CellInsertionPointCell->None. (You can get WolframAlpha just by typing = as the first character in a new cell.) And the Predictive Interface can be disabled by the "Show Suggestions Bar after last output" checkbox on the Preferences, Interface.
The new Input Assistant (ShowCodeAssist in the Options) is a problem for package developers. Previously one could use Ctrl+K to complete an entry and, if the function format was used as the initial portion of the usage message, Ctrl+Shift+K would complete the entry with a labeled template. But that no longer works in package design. On the Workbench Raw Function page there is a "Syntax Templates" entry and I assume this is the new way of entering this information. However, WRI has given ZERO information on how to enter this information and the few guesses I have tried don't work - and take too long to check. I think I did once ask them about it and got no answer. This is pretty bad treatment of developers since this is a major interface feature.
They say they have new ColorData schemes, but I don't see them.
If you want the ColorSchemes palette to remember its position and state, you will have to go into the Wolfram folders and give the user control of the file - at least on Windows.
The new Vector Analysis functionality is fairly nice, extending to higher dimensions.