So I'll preface this by saying I have a very large 450GB Aperture library. It works just fine on my Mac Mini, and is lightning fast on my new Retina iMac, both in Aperture and iPhoto. I opened Photos and it went through the conversion of the library, then just closed without an error message. I tried to reopen it and got Assertion failure in -[RKBipJob updateFromJob:], /SourceCache/PhotoApp/PhotoApp-209.52/lib/redrock/Image/RKBipJob.m:68 Invalid parameter not satisfying: [self isEqual:job] abort() called Reset everything back from backup of the library (everyone did backup before upgrading, right?). I did a permissions, repair and rebuild on the Aperture library, made sure I had no referenced files, and opened Photos again. Same thing, but this time I did get an error message, and it looked like it was after the conversion completed. Now when I open Photos, I see my photos for a few seconds, then get the same error. Tried holding down option-command when opening Photos, and it did a repair on the database, but then still got the same error. By the way, side bug--your library is renamed with a different extension that adds "migrated" so that breaks screen saver that refer to the library, and iPhoto as well until you point to the file (hold down option when starting Aperture or iPhoto). (Actually that made me check to see if Photos is available as an option in Desktop & Screensaver, and it is, so it looks like the Photos library was created--just can't open the app). Anyone else having issues? I'm going to try it with a smaller Aperture Library (you can export to a new library in Aperture) and see what that does, but if I can't have the whole library, it's not that useful.