It is. If you've never played a Fallout game and know nothing about the lore, it's a 7/10 at its current state. It has a single player questline, with tons of side quests, good for at least 30 hours of gameplay. But likely way more.

On top of that it has base-building, exploring (giant map), looting, crafting, weapons, armor, modding said weapons and armor, and a ton of different ways to build your character.

Then of course there's the "MMO" side to it. Daily, weekly missions, public events, regular events, special ops and since recently an "expansion" called The Pitt (which is basically a large special op on a different map), and other players with their own bases and trading posts.

However, if you are familiar, and more importantly a fan of Fallout games, you are likely going to be pissed off. Fallout 76 makes no goddamn sense lore-wise, and they changed a alot of mechanics to fit the "multiplayer MMO" aspect of it. That said, I am a huge fan of Fallout, and I just see 76 as a nonsense-noncanon-Fallout-sandbox, which makes it okay in my mind.