In many ways it remains ahead of the curve. Kids that grow up making games in Roblox rarely survive the jump to a dedicated engine because Roblox is just so much easier to develop for in nearly every aspect. One big thing I've heard is that instantly getting working, robust online multiplayer by default baked into the engine is a major plus.
I would call multiplayer out of the box the defining feature for sure.
It's challenging to get networking right, and the effort required doesn't get all that much smaller just because your game is smaller.
Most engines do come with a networking framework or layer these days but Roblox gets to assume a bunch of things an engine can't, and as such provide a complete solution out of the box.
They originally accomplished this with an interesting approach to netcode you couldn't do today.
Everything was replicated in the client and server. So you could open Cheat Engine, modify your total $$$ on the client, and it would propagate to the server and everyone else playing.
They only fixed this in 2014 with FilteringEnabled/RemoteFunctions but that was opt-in until 2018 and fully rolled out in 2021 (breaking most classic Roblox games). This also made games much harder to develop.