harpreetOsingh's solution WORKED!!! ALL my apps, music, photos, etc. came back...only my contacts remain elusive (they're shared on my iPad mini, though, so there must be a way to get them to copy to my iPhone...then I'll be in business, on IOS 8.4.1 (I'm NOT going to try 9.0 again until it's fixed!!).
MANY, MANY THANKS TO HARPREETOSINGH FOR ALL YOUR HELP!!!
It shouldn't be up to Apple users to fix Apple's mistakes, though. Where are the Apple Reps in this discussion?
By the way - for anyone who hasn't backed up recently - your photos ARE accessible in your phone, even when you're at the dreaded "Slide to update" screen. Windows 10, at least, finds the iPhone when connected to it by wire, even in that state, and considers it an external drive.
All your photos are there, and accessible. I just created a new folder on my desktop {"iPhone backup photos Sep 17 2015") and copied all 1100 pictures to the new folder. No matter what, I'd still have my pictures. As it turns out, when iTunes finished installing ios 8.4.1 on my phone, it asked if I wanted to do a restore from backup (my last one was last November, but I hadn't made a lot of changes in that time) or as a new phone. I opted for the restore-from-last-backup, and the phone is pretty much back to normal, including every one of my pictures (I'm not sure how that was possible, as a lot of them were taken since my last backup...how did they get back on the phone??? I don't care...they're there!!).
BTW, I followed harpreetOsingh's solution to the letter, and it worked perfectly.
Best of luck to all!!