Luckily there is a log with every ever installed, upgraded or removed package. From time to time the log file is archived and the latest can be always found at /var/log/dpkg.log. I wrote a simple script that parses all the log files, including the archived onces, and extracts the packages names.
So one can simply do
$ sudo apt-get remove `./dpkg-since.py 2015-01-01`to clean up the system from anything installed since the beginning of the year.