Unfortunately most of Roblox games are just attempts to siphon your money by buying Robux. Their target market, kids around 8, beg their parents for Robux so they can buy some stuff in one person's game.
It's incredible how much money they make through tactics that make many of their games not really enjoyable unless you spend a lot of money in them.
Just remember that the average age of a Roblox player is like 8, so in-depth RPGs or complex sim games probably won't get a lot of traction.