Well, it's about time. Windows 10 Mobile users have been unable to take decent panoramas since the death of the old 'Lumia Panorama' utility (and that wasn't great), but the functionality's now built into Windows 10 Camera, at least if your phone is on the (Insiders) 'Redstone' branch of the OS, which is about to become the Windows 10 Anniversary Update for all compatible devices. The resulting panos are around 1500 pixels in height, so a typical panorama would end up about 10000x1500 pixels, or 15MP, which seems about right in terms of a quality/size penalty standpoint. After capture, the panoramas are just regular images and can be edited or shared in the usual way.

To get this new feature, just update your Camera application in the Windows 10 Store right now.

Panoramas are only captured with the phone in vertical/portrait mode - this makes sense and is the most natural way to do this (I do the same on the iPhone and Android):

Panorama mode joins Stills and Video modes in a three way selection...

Movement has to be in a 'left to right' mode and you do get prompted to 'tilt up' or 'tilt down' if you're drooping your grip too much.

Results are pretty good, though obviously I need to test this a lot more....

Around 12MP, a typical panorama, shot this morning at my local park....

A great addition quite late in the day before the Anniversary Update hits. 

PS. As per the comments below, there seems to be some device dependence too - more data points welcome. Obviously this all works on the Lumia 950 and 950 XL, but how far down the chain does it go?