To elaborate a little more, while he's on New Krypton, he's gotten embroiled in a civil uprising between some of the various Guilds that make up their culture. Since he grew up on Earth and therefore never took up a Guild of his own, Kal got to choose one, and ended up joining the Military Guild, if only to keep a closer eye on their leader--the recently-freed General Zod (the Kandorians weren't around when Zod tried to take over Krypton, so they still revere him as a hero, and they don't believe Kal's pleas that Zod is evil)
Back on Earth, a few different heroes have stepped in to watch over Metropolis, like Mon-El and Steel (as mentioned). There's also a new Nightwing/Flamebird team, this Nightwing actually being Lor-Zod/Chris Kent (the Kryptonian boy from "Last Son"), and they're busy tracking down a bunch of different 'sleeper' Kryptonians that Zod had left on Earth during their invasion back in "Last Son," in order to take over the Earth in secret.
Also, a bunch of Supes' villains were rounded up by the Kryptonians and chucked into the Phantom Zone, but in doing so, they also killed a few policemen who were trying to stop them (which is what led to the big conflict that forced them to leave Earth) A few of them are still running around, particularly Lex Luthor (who has been freed from prison by General Lane in order to come up with anti-Kryptonian weapons and whatnot in case they try to invade again) and Brainiac (who was 'captured' by the military and is basically laying low until he find the right moment)
That's the long and the short of what's going on with Superman these days.
