In 2006, I could download the Roblox app and bam, I would play thousands of 3D multiplayer games for free that loaded near instantly. With fully destructible buildings and dynamic terrain. Somehow I didn't get viruses from remote code execution.
That was groundbreaking at the time. In that era, I'd have to download Steam, buy individual games like Counterstrike, and the wackiest thing would be the "surf" gamemode. Most games I'd buy on CDs. I certainly couldn't knock down entire buildings with grenades.
If you contrast with Second Life/Habbo Hotel, you could walk around and talk to people I guess?
The community that spring up around it eventually carried it into total dominance of gaming for American children, but the basic parts of the engine like "click button, load into game, blow stuff up" were a decade ahead of the curve.
Also Blockland cost money, Roblox was free.