I really liked the first game, but it was very Spartan. Both gameplay wise and in interactions it was really just the most basic RPGmaker fare, though with much better artwork and a better concept than most.
For now I've only played a little bit of the sequel, but I really love the clear ambition the dev had to improve. The gameplay and presentation are better already, but there are actual conversations and connections between events that make it feel more fleshed out.
Mio could get corrupted in the first game to the point where she would abuse her hero status to have sex with random women in the city, but the "corrupt" harem ending where she stayed in the other world is obviously not canon. Now you can see a much more natural corruption take place, which feels more like Mio accepting her lust while not completely losing her mind like in the original.
Also so good to have Seira/the priestess come to Mio's world. They were so cute together and I hated how they only didn't get separated in the "bad" ending. Though Ruka, Mio's childhood friend, looks like a great foil... good old love triangles.