I got the same 500 error, however there mus have been something wrong with my permissions because WordPress nuked my entire root directory! When I FTP’d in I expected to see all my domain root folders but all I had left was the domain folder for the wordpress instance I was upgrading!
Not only that but it looks like a skeleton, wp-content, wp-includes etc. are all empty.
I took backups of my wordpress instance before upgrading (thank god), but not of all my other domains. Unfortunately they’ve all been ticking over on autopilot for ages now and the backups are pretty old ??
Poor backup routines are my problem but an auto-upgrade button that nuked my entire site collection is another one entirely.
PS, I’m sure there wasn’t any warning about disabling the plugins on the upgrade screen.
