Okay, so I've just got SC15 and it is great. However, you still can't trend multiple segments in one report (e.g. if you want to do a report of traffic for today with one line for all visits and the other for uk visits only - you can't).
GA could do this well over a year ago I'm pretty sure!
Instead, I have to do several reportlets next to each other or do the report in Discover (which I can't automate).
Would be a great addition for MANY reports!