One systematic way:
- Go to the IFDB.
 - Search for games tagged 'twine'. Hope like mad that you don't get stories about string.
 - In the ickle drop down menu at the top of your search results, select 'Highest Rated First'. 
 - Hope that people's tastes are similar to yours, and are indicative of objective quality, whatever that is in IF.
 
Less systematic way: look for past year IFComp games, or other competitions, and seek out highly rated Twine games. Again, assume that your idea of 'good' is similar to other people's.