I just finished the book and had to look this up because my brain wouldn’t turn off after that last chapter. The short answer is yes, it ends on a cliffhanger, but it's not the kind that leaves you totally lost—it’s more of a ‘what’s next?’ than a ‘what just happened?’. The final scene has Sung Jin-Woo getting that mysterious notification after the double dungeon, and the book cuts right there. It feels like the end of a TV season where the status quo has just been permanently shattered. You know he’s changed, the world is bigger and weirder than he thought, but the immediate 'how' is still a question mark. I didn’t mind it because the whole volume builds such solid momentum; you’re already hooked on his progression, so the cliffhanger works like a promise of more to come rather than a cheap trick. I grabbed volume two immediately.
Some folks online seem really annoyed by it, calling it manipulative, but I think it fits the serialized origin of the story. It’s structured like a great episode break.