So far they've hit the most popular of the early batch of adventures from Sierra and LucasArts, looking back at King's Quest I, King's Quest II and III, Space Quest I and II, Maniac Mansion, Zak McKracken, and Indiana Jones and the Fate of Atlantis.
There's still eight months left, and a lot of classic adventures to cover, so it will be interesting to see what other games IGN plays through. They certainly can't go wrong with playing through any of the LucasArts adventure catalog, as we so thoroughly showed in our own LucasArts Secret History features from a few years back.