[Updates below in BOLD.]
On loading SSMS for the first time, I noticed a few things. First of all, the row(s) affected message is now prefixed with information on the instance and login relevant to the query execution. This information is already available in the status bar. Why are they spoon-feeding it to us in the row(s) affected message?
Next, I noticed the region-like behavior that has been added. You cannot define your own regions, but the more typical code blocks you would want to hide/show are supported by default. (Except block comments.)
Error highlighting is not all that perfect just yet. Sure, it identifies common syntax errors and undeclared variables, but it also yields a false positive on perfectly valid function names, such as OBJECT_SCHEMA_NAME(). [Note from Connect #311086 : this will be fixed.] Notice also that syntax highlighting has taken a step backward. sys.objects, for example, should be green; OBJECT_SCHEMA_NAME and OBJECT_ID should be pink. [Note from Connect #311089 : this will be fixed.]
And finally, I got to play with the much-anticipated IntelliSense functionality. I already knew that it was not supported for many syntax operators (primarily SELECT). It was pretty fast in my tests against a local instance, however I have not played with it yet remotely (performance here is the main reason I can't use Red-Gate's product). I was disappointed to discover that in a query with a single table/view, if you do not use an alias, the auto-complete list includes everything under the sun, making it very cumbersome to find and select valid column names. [Note from Connect #311088 : they are trying to make this better, including sorting in CTP6.] If you use an alias, however, this allows you to narrow down your list considerably. Not the most intuitive thing in the world, but I guess I will learn.