I guess that depends on how you look at it.
It would currently be my favorite game, based on replayability, although it wouldn't be the best coming from the first-hand experience. Hearthstone can be played in extremely high doses without feeling much less tiring. Try playing any game that are story-based, more than 2 or 3 times, and you'll see the games through different lenses.
Still, nothing is ever going to compare to the first time i stepped into the World of Warcraft. Experiencing that vast world for the first time ever is something that probably never will be beaten.