Originally posted by me in the official Aptana forum solution for those who want to rollback from 2.0 to 1.5.
For those, who want to go back to Aptana Studio 1.5 Eclipse plugin with Aptana PHP support there are the links:
Aptana 1.5 Studio Eclipse plugin: http://update.aptana.com/install/studio
Aptana PHP Dev. Env. 1.1: http://update.aptana.com/install/php/index.html