I'm personally of the opinion some sort of save is desperately needed. Not a "quicksave" system, or anything, but something to be able to save progress - end of the level, perhaps, or something similar. Maybe even a limited number of saves. which can only be refreshed by reaching set points. (go up a level, a previously used save slot becomes unlocked again?)
As it is, the demo is not enjoyable. Its not "frustrating" - it rapidly becomes tiresome, a chore, and having an hour or two, even three hours of gameplay chucked away by one random encounter, throwing you right back to the start is not fun. its not beneficial to gameplay. I have better things to do with my life that return to the start every time some trivial event goes wrong
Replaying the same thing, again and again (Start again, open door, turn right, run along, go through doors, go get the keys, go to the same places with chests, try to find some decent bits of gear etc etc) does not contribute to player enjoyment, and I feel that it dissuades players from playing the game. In terms of design, marketing, and production, it harms the product.
I personally feel that there's nothing "hardcore" about that, as a design choice. When, for instance, I spend 2-odd hours slowly working my way through the entire first level, carefully avoiding most opponents, only to be confronted by one in padded armour, with a two-handed sword which instantly springs to attack (and of course, gleefully hacks me apart) right at the end of the level, it doesnt feel "hardcore". It feels spiteful. Dying at that point, knowing I've just wasted 2 hours for nothing, my reaction is "f*ck this sh*te". That is not good game design. Failure should make the player think "Damn! I want to go back and beat that!", not "Oh, hell no. I have to do all that again? Forget it. I quit."
It particularly leaves me worried about similar design decisions in Sui Generis will leave it an unplayable mess, forcing players back to a starting stage again and again. It was crap gameplay design in the 80's, its crap gameplay design nowadays.