You cannot get all your logins, session time, IP address, etc. This is what you have a right to get out of a EU based company. Yes, this means that as a business, it is pretty hard to comply with the law.
A simple but perhaps inconvenient way to verify this is to be criminally prosecuted for something where your Google account is relevant. Google will hand over what they have to the prosecution, and as the defendant, you'll be entitled to see the evidence. (I've not tried this and don't recommend it, but do know someone that this happened to, and have examined the contents of the provided CD.)
DataLiberation is mostly a PR site, and it's main use is migrating what data Google feels is useful to you, not finding out what Google knows.