The merging of more than 60 Google privacy policies into one has been criticized by privacy advocates, users and governments. Critics argued that the sole purpose of merging the privacy policies was to get an even better picture of a user's online activities to drive ad revenue for the company. The inability to reject the change, other than to close down the account has been criticized heavily as well.
Google users have only limited options to prevent the changes from taking effect for them personally. They are able to mitigate the effects somehow, but there is no way of preventing the changes completely.
It is recommended to log out of a Google account whenever it is no longer necessary to stay logged in. While you need to log in to check your Gmail messages for instance, you do not really need to be logged in when viewing videos on YouTube or searching on Google.
You can get a rough overview of what Google knows about you on Google Dashboard. It lists the services that the logged in Google account owner uses. Some services provide options to turn tracking features off. This is for instance the case with the Web History feature in Google Search.
In the end, you have only three options. Live with the changes and do nothing about it, accept the changes and try to mitigate their effect as best as possible, or switch to other service providers or alternatives instead.