Upgrade failed - what needs to be restored?
That should do it!

Auto-updating to 2.5 is causing a few people headaches, mainly because people are bumping up against their php.ini setting limitations. It's a pretty significant update, requiring pretty significant server resources to handle the transition.

Once you've successfully rolled back, I'd recommend performing a manual update. This takes a lot of pressure off of your server, and only leans on your server resources to run the database migrations (which definitely shouldn't cause any overloads).