Look at instagram.com/drawn_tdg, or instagram.com/moleculecure on an iPhone. For those IG galleries to work, photos have to be loaded in a very particular sequence, and the Camera Roll stored photos, all of them, in exactly the sequence stored (whether by taking the photo with the camera, or saving it off of a Message or Email, etc.)
"Recently Added" doesn't do that. The photos may be recent, but they are not sorted in "order saved". I have yet to determine the criteria being used.
The various "Photos" collections organize by location (not useful in this case) and by "date", but that date isn't the date SAVED TO THE DEVICE, but rather some internal metadata date stored with the photo. Not useful.
Nor is searching aided by the Collections. Photos are visual, and most people relate to them visually (It was next to this photo, or before this one).
To build my IG gallery, I save photos, take pictures of drawings, use various apps to edit and slice and store my drawings in sequence, other apps to load photos and annotate or add borders... an entire array of photo-related Apps and sites, all built around the intuitive and sensible Camera Roll. I need to work with photos in the sequence stored, I need to work with photos older than 30 days.
In short, an entire ecosystem is built around the Camera Roll, and by removing it, the food chain is broken. It's as if suddenly the trees in the rain forest had been removed. It breaks the entire ecosystem. Telling me that the trees are not really MISSING, they've just been reorganized according to other criteria like size or economic value or that they are now sorted horizontally onto flatbed trucks is rather beside the point.
So, I can wait I suppose for tumblr, twitter, facebook, instagram, phonto, pixlr, instatiling, and several other Apps and sites to all conform to Apple's new photo paradigm, or... Apple can bring back the Camera Roll. (Which, they apparently tried to do with 8.0.1. I guess we'll have to wait and see.)