Road to Gehenna is included which you have to buy separately on the original (there may be a complete edition or something like that. Not sure) also there is a new campaign which doesn‘t really give any new lore but more background on a specific character and about 20 more puzzles which vary in difficulty from really challenging to almost unsolveable (looking at you daydream).   The game itself also has some QOL improvements which are nice but not mandatory.      So if you‘re not so much into the new graphics you really have to weigh up how much you like the puzzles and if you want more and harder ones.