Second life is trying to be a metaverse in the style of snowcrash; it’s one big world. Roblox is more like Newgrounds, where you have a bunch of distinct games or experiences that you select from a menu, but skins and currency and whatnot are portable between the games.

Easy to dev for. Runs on a potato. There are many maps and modes.

Kids in current year like it

The main difference is there that Roblox games are fun.