Taste is always subjective. I may love something that others think is trash and vice versa, and my scores would reflect that. I, for example, don't like G-senjou no Maou and gave it a 7, while many consider it a masterpiece.
Of course, if there are hundreds of low scores, something is not right with that game - but even that is not certain, as low scores can be due to anything, a poor story, bad characters, it being LGBT [yeah, there are people who would give low scores just because of that], etc.
I think the best way to find out if a VN is good is by reading it yourself, at least the beginning. If that's not possible, look for in depth reviews where the author justifies their scores. What I also do is to see who is the author of the VN and if I like what they write.