I have played 13 of the Mystery Case Files games, but I know there are more. A couple were too "brutal" for my taste or were too easy during the Demo play so I didn't buy them. It is a good series, well done, long games with tasty and challenging puzzles galore. I have replayed a couple of them.
Mystery Trackers is another good series, and I have played 12 of those. Again, some can be too easy, like MCF games, but most are good and a few are great.