I received an ipad air in the mail today. Before it arrived I went ahead and did an icloud back up and thought I might go ahead and do an iTunes back up to my computer as well. I got the new pad and went to restore from icloud. Everything was in order and thought all was good until I went into the pictures. I only had 241 on the air and on my ipad 4 I had over 600. I erased all content and tried again. Same result. I really had no idea there was even an icloud photo library at this time. I just knew that the camera roll came back with 8.1 so I turned on the Icloud photo library and it took the 241 pictures and I was able to view(also on icloud.com) but the others disappeared. I still had the 600 photos on my iphone but they were gone off the ipad. Also when I turned on the icloud photo library, the camera roll was gone too. I was frusterated to say the least. I ended up hooking the ipad air back to the computer and iTunes and restored from my backup at 9:41 am and it put all the original 641 pictures back on and everything in working order. I would recommend anyone who is into their pictures to backup to your computer. I have lots to learn and lots of questions about the new icloud photo at this time so I will leave alone for a bit.
iCloud restore doesn't restore all your photos at once. The Photos app on your iPad will download the backed up photos one by one. You just give it more patience, after a few hours all your photos will be back.