I play games mostly with a goal of having a pretty broad knowledge of the video game medium, past and present. That is, I want sort of a semi-encyclopedic, enthusiast level knowledge of gaming as a whole. For that reason, the below is often true of me...
There are games that I consider all-time favorites that I've only ever completed once.
But also I get pretty in-depth with my favorite series, so I think that makes up for it. Also, I try to at least give most games/series a try, even if I think I won't like them, if they seem to be of some significance to the history of the medium. In the case that I don't like it, I at least have a legitimate opinion, and in the case that I do, I've just expanded my tastes and surprised myself. Pretty much a win/win.
The past year or so, I've been trying to investigate important Japanese stuff that I've missed over the years. Still haven't tried a true SMT yet, so that's definitely on the chopping block. Looking forward to it. That and seminal Atlus blockbuster P4D, of course.