Dusted off my 635 just for this purpose. I have to say, after the whole process, I'm NOT hating it at all. For 512MB of RAM and the S400, it's running fairly smoothly. The new Music App isn't there, so xbox music is like it was when 8.1 was first released (cue war flashbacks). In setting the background, your tiles become actually transparent while there's an image sitting in the background, the accent color stays but becomes less opaque. I thought I'd hate it but it actually looks pretty good. One problem is that for both lockscreen and background images, there's no way to adjust how you want it to fit, you just have to take it as is, so good luck if you have a full fledged wallpaper you want to crop.
Also, the default camera app is kinda nice. Still playing around with everything but those are my thoughts so far.