I completely agree to you on this point, filtering by that would be pretty nice, but from what I could see it's not an option right now.
A "workaround" would be to go to your achievement page
N1ghtshade3's Achievements, go to filters, select all of the not-won achievements and then filter by "missable, unobtainable and discontinued". Then... Just avoid these games. Meanwhile, I will forward this to a site dev and see if an option to filter by game flags can be added
Hope I'll see you around on the site in the future. It's always great to see more active people in here :D
Game on!
-Red