I guess people were expecting a pixel to pixel remake a la Ninja Warriors Once Again. Honestly, the reception is kind of reminded me of Ultra Super Street Fighter 2 HD Remix. At the time, there was some mixed reception, but over time most people grew to like it or didn't have a problem with it. What probably helps is that when it got re-released on Switch, it allowed the options for the original visuals or the HD version. Then again, that one had some additional modes as well and two new characters.
Looking at Night Slashers, it's going to go up to four players instead of the arcade version's three. So we might see a new character. The game is definitely adding new combat and refined combat mechanics in combos. That much is obvious. I do wish that they allow you to revert to original style for those that want it. I do appreciate that you're allowed to change the colors of characters outfits. That's an option I always appreciate.
BTW, did you ever get to Ninja Warriors Once Again/Ninja Saviors yet? No rush if you haven't yet. I know the game is still at $20, so if that's too much for you, I won't blame you on waiting for a sale.