I like to collect games that are historically significant. Often, the most important games aren't well-known, or even well-made, but they introduced concepts that other developers ran with. Whoever does it first, does it worst. But that's okay. Somebody had to go first. And even dead ends are fun to study. Maybe some of those dead ends were just ahead of their time?

I also love hidden gems. Games that spent their money on development rather than marketing. Passion projects. Games that would have taken off if they came out ten years later, or games that missed their market by ten years but exemplify their core concept. Games that were just a bit too ambitious for the hardware of the period; or games that executed a simple concept perfectly, with no fanfare, instead of pushing the envelope.