Is this just a unity conversion of old game or something new have been added too?
From what I've seen so far, it's a unity conversion from its flash engine origins with some new additions.
1. The unity game starts with the option to choose the screen resolution and windowed or full screen. There is standard resolution 1280x1000 and the 2k resolution is 1707x1333.
2. The unity version does have something that I think wasn't available on the flash version and that is a speed up fight option. Fights can be speeded up to 3x speed, however, there is no normal speed. Each fight will show you battle tips before you begin.
3. The sounds, music and voice acting (sex moaning) are carried over from the flash engine.
4. In my opinion, the game runs smoother compared to the flash version.
5. Within Lilith's diary, in the secret memory, you can revisit each encounter with the monsters. A nice feature is that you can place the mouse cursor on the hearts below a monster and a video preview with sounds will play. From there you can click to revisit the encounter in its glory.