I'm in the process of switching my user base over to the new iOS version of ArcGIS Collector. Some of the changes and improvements are excellent - ability to label features, directional arrows, auto sync etc etc are a real improvement. However, I think the user editing experience has gone backwards a long way, specifically for lines and polygons.
In the 'Classic' Collector, a line or polygon feature could be drawn on screen by tapping on screen for each of the feature vertices, and then saving the feature. However, in the new version, the user needs to pan the screen so that the vertex to be created is aligned with the centre cross hair, and then tap 'create point'. This is hugely inefficient and quite frustrating to use, especially if you're working in a moving vehicle or helicopter (as my user base generally are).
A huge enhancement to the new version of Collector would be to allow the user to revert to a similar editing experience to the 'Classic' version of Collector - specifically where they can just tap on the screen to create a feature vertex.