I played a ton of NES games back in the day, but I am still getting into the gems on the SNES and Genesis. These are great systems. I'm not too interested in generation 5 at the moment, but the games that look interesting to me (that I might actually play one day) are either RPGs or 2D games like Symphony of the Night.
There are also all of the games on handhelds over the years. There are a lot of great games there that I am still discovering.