Spot on. I think the art direction is fine (although I think that the camera work is a bit spotty, as it reminds me of a more jarring version of dangaronpa if I'm being honest).
For me, here was what I thought: the intro should just straight up be dropped in all of its capacity and it should simply start with you being in the class itself, or start with the broken down group of people that MC was talking to (as their conversation I thought was actually pretty interesting, and brought up ideas that weren't really addressed ever again in the demo).
The voice acting is a bit awkward overall, and the demo doesn't really give a good representation of what the actual game play loop would be. If it's going to only be talking primarily, then... Yeah, the dialogue needs a bit more refinement.
I think the premise could be interesting as a subject to tackle, but there wasn't enough for *why* they were Historians or anything-- we don't even know why they were selected and based on the general dialogue, there isn't even really anything that you could begin to piece together as to why.