If this game is a remake of lust grimm, then there's no need to play the older version, right? or are they different and both canon?
The original game had pretty different game mechanics, much less forgiving than the remake version but more fun in my opinion.
The other main factor is that some h scenes are different, as other people already pointed out.
The remake also contains many more scenes and some are animated.
The two games also run in different versions of RPGMaker.
I honestly recommend you to play the old version first if you have the patience to go through both games, since the old version gives a very different vibe (and I think a better one) compared to the new one.