I vividly remember playing Flashback back in the 1990s -- the excitement of postal orders, installing from floppy disks, the tracker music, the amazing animation.
Fortunately, this conversion retains the original game. There's no "upgraded" graphics to annoy you. No "director's cut" of extra level segments. The original is there, warts and all.
The game is quite short. As an adult, it's definitely more linear and straightforward than I remember.
The conversion is adequate. The faux-CRT filters are, as others point out, completely optional. The bloom filter has a nasty tendency to turn itself back on.
The biggest let-downs are the music and the controls. The music appears to be some MIDI files, probably from the Genesis version (?), rather than the amazing Amiga tracker files. The controls are not configurable -- annoying, since I'm too used to WASD these days.
Of course, they could've done a Linux build too, given it uses Unity (AFAICT).
All in all, it's definitely worth buying, especially when it hits sale.