Of course, there's undoubtedly more content coming. PvP content wasn't included at launch, but is scheduled to show up in a free patch. And the real-money auction house (which may end up being the real legacy of Diablo 3) has been delayed past not only launch, but its planned debut date as well. There is already an in-game currency auction house up and running, but Blizzard wants to make sure the servers will stay up before real money starts getting passed around. If its current efforts to keep the game up are any indication, it may be a while.
Even without those features, however, Diablo 3 is a masterpiece. It advances the classic form of Diablo 2 past the World of Warcraft era and diablo 3 account, including its own versions of mechanics like crafting and the Auction House that worked so well in Blizzard's MMO. At the same time, it remains Diablo - Torchlight added a pet that will sell items for you, among other innovations, but Blizzard has remained characteristically traditional on that. You go out, you kill monsters and pick up loot, you return to town to buy, sell, and upgrade. Rinse and repeat, forever and ever, amen.
These days, dungeon crawlers are everywhere - you can play them on any console, any operating system, any place to sell diablo 3 account smartphone you can find. They're like slot machines in Vegas: You'll find tons of them, and all of them will give you that addictive rush of killing bad guys and leveling up, of dropping the coin and pulling the lever. With Diablo 3, however, Blizzard's running the best room in town.