I was very hopeful that 9.1 was going to get the 9 series over the hurdle to fewer bugs and solid features.
Layer and alpha channel TIFFs will be welcome, if the work well. But have haven't dug in very deeply because a number of bugs that I've reported and had confirmed are still not fixed. And they are not huge problems or giant features:
206153 - confirmed 12/9/15
Editing Print Templates is Too Dark The list of available user print templates is too dark to see any except the highlighted one.
212339 - confirmed (2/17/16)
Floating tools don't remember their size after being collapsed.
207920
The icon in the upper left of the first thumbnail in a stack shown in the browser and used to collapse/expand the stack does not always appear.
Sadly, there were a lot of improvements to tether, but I don't use tethering. But we still don't have image stacking!
Frustrating and sad. The core of C1 is so good - but the supporting parts are not at the same level.