I've never actually played Roblox, but the sense I get from it is really similar to the early Newgrounds flash-games scene. Seems like there's lots of creativity, a community of people always working on new things, and tools that are simple enough to serve as an on-ramp for people with very little experience.

Much like today's upcoming generation of animators have their roots in Newgrounds, perhaps sometime a decade from now we'll see a new generation of game developers who got their start in Roblox mods.