Starcraft and Diablo are considered one of the classic franchises in their respective genre. For those that have not taken the plunge on the latest releases, Battlechests for both games complete with all their expansions are now out on Datablitz, and it's at a good price range too.
Both games are still being heavily supported by Blizzard.
In Diablo 3, they have seasonal mode which gives players the opportunity to play the game all over again but with new gear sets to give more experimentation and variety in builds across all classes. They are currently at Season 9. Not only that, Diablo 3 will have its first class pack bringing back the iconic Necromancer class to the game.
For Starcraft 2, a lot of changes have happened since it's release in 2010, and thanks to the expansions Heart of the Swarm and Legacy of the Void, we are given new units and campaigns for each race to finally complete the Starcraft 2 narrative that started years ago.