It’s not shocking, when you consider the level of graphical fidelity they’ll be pushing on screen.
The more detail you add, the lower the framerate, on any given hardware. They will be balancing “oh my God!” level graphics, with playable frame rates. The fact they’re shooting for such a relatively low frame rate, shows how hard they’re pushing the hardware.
This is more arcadey, but I recommend giving Cave Story a go. The story is rich, the worlds deep. It’s a great game. It’s not the same genre, but for me, it has a similar vibe.