I wouldn't say it's super original. The whole giant robot verses giant monster thing has been done before, and the ending was pretty much the exact same thing as The Avengers or Independence Day.

Not to say I didn't enjoy the hell out of it, but it's not meant to be a big, complex universe. It's just a big, dumb fun movie that doesn't complicate it's big draw with a crapload of lore and characters. They explained everything you need to know in the opening minutes of the film. That's literally all there is to it. A prequel wouldn't make sense because the kaiju weren't as big and numerous as the movie and the Jagers didn't all get wiped out at once, it was a slow draw of attrition. Not exactly super compelling if you're trying to top the set pieces of the original.

A sequel makes more sense, although I don't think they should. There's no more Jagers and they closed the rift. Just making up mumbo jumbo to work around that is a dumb cash grab. Like all the seven hundred carbon copy Marvel movies.