Overarching filter is Workspace(s). That's great.
Out of the box filters/dimensions are 1) Lead country and state 2) Email Send, Program, Smart Campaign 3) device type and OS
Filtering works via searchbox, manually selecting/picking each item. So no filtering by "name contains", wildcards or regular expressions. You'll end up with a lot of clicking. Sadly the filter settings are not saved on the QUICK CHART function nor anywhere else, so that clicking needs to be done every time. I sure hope Marketo will improve the UX around this.
You can add another 10 dimensions - although I haven't seen any more documentation on this, which field/data type this supports.
If anybody hears this supports other data types than string, please let the community know. I'd like to see at least date, which can be collapsed/collated by month, quarter, year. If date/time are only interpreted as string I guess one needs to start building additional fields around those, like YY-QQ or YYYY-MM to get valuable insights, e.g. for a "Lead Created Month".