The bad news is, there is no camera roll in iOS 8. In its stead, you have new folders like “Recently Added” (shows recent photos that are about a week old), “Videos” (which has all the videos you record), and “Recently Deleted” (for restoring deleted photos not older than 30 days).
But “Camera roll” is gone. How to get it back? Sadly, unless Apple decides to re-introduce the camera roll back in a future iOS 8.x update, there's no way to get back the “camera roll” album.
Camera Roll Missing in iOS 8? It's Gone. May be Forever.
Camera Roll was the go-to place for all the photos and the videos. Up until iOS 7.x, it stored everything and since it wasn't segregated (only chronologically ordered), you had instant access to thousands of photos and videos.
But let's first get used to the fact that it's not available in iOS 8. Dig through the Photo & Camera settings in iOS 8 and there’s absolutely nothing that can turn on or bring back the Camera Roll.
A lot of people are complaining about this and while it’s possible that Apple might re-introduce the camera roll album, I wouldn't hold my breath. Apple sometimes forces a change through disgruntled users. (May be different under Tim Cook, but we'll not know till at least a month from now).
Use Other Apps
Meanwhile, if you want this camera-roll facility (if only to view all the photos in one seamless album-view), you can try a variety of third-party photo album apps.
There's work involved though. You will have to import all the photos from your Photos app to an album in the photos app.
Frankly, I have yet to see one decent app where I can somewhat replicate the Camera Roll experience. So this sounds like a shot in the dark but I am hoping some app comes with a decent solution.
Get Used to “Moments”
All your photos are still accessible from the Moments view. To view them, just tap on the Photos menu. You’ll either be in the “Collections” screen where photos are organized and segregated by a time period (days or a month or by location). Tapping a listing will show you the Moments. You can still scroll through (up and down) to view all photos just like you'd with Camera Roll.
Using Photos in Other Apps
This will change but for the moment, when you try to insert/access photos from a third-party app (like Whatsapp/Instagram), you might not be able to pick photos outside the Recently Added album. This is definitely annoying but this is not a bug. The app developers have to use the new Photos API to let users access all photos on their iPhone/iPad from within the their (third-party) app.
Update: Instagram seems to be updated to fix this. Dropbox still shows photos only from the Recently Added album.