And more. Yes the graphic might be outdated and not as fresh as you think. And yes the game is "unfinished" and many upcoming Slaves were canceled and so on. But this game has a Nostalgia Bonus for many Oldies (like myself). Though i think for newer players it is not a bad idea to try it out.
A lot of the problem is that slave maker was made for an internet otaku audience circa 2004-ish. Younger Gen X'ers and elder millennials. Consequently you get a ton of characters that would have made sense at the time from properties like Ah! My Goddess! and Tenshi Muyo.
As a result a lot of the plundered artwork used for it is....dated. Not bad, per say, but something made to be effective on the kind of bandwidth a 56k modem might provide. Or, if you splurged, and lived in the right places, a fancy DSL line. And it was meant for the display ratio and resolution you'd have on a CRT monitor.
There was also plain old bloat- the developer was super ambitious, as is often the case with fan eroge, and over estimated their interest in continuing to work on the game.
If someone were to do a re-re-(re?)-make it'd probably require the ability to save templates (so it automatically goes through a set routine instead of making you click 10 extra times) and, to repeat myself, a bigger variety of art. You kinda accepted that there'd be a lot of repetitive gameplay back in the day because that was the norm but repetitive gameplay + repetitive art isn't good design these days.