I'm quite a huge VN fan, to the degree I even made one which in part delves into the history of VNs. I'll list my top 5 (not in order) and pray that either somebody else here has heard of them, or that anybody reading this is interested enough in giving one of them a chance.
1) Narcissu: For a VN that's both free and short, it's amazing how year after year I only appreciate it more. It might seem cliched to say, but I've never seen the subject of death covered better in any other VN. It's the type of tragic story which by its end makes you grateful to be alive.
2) Sayonara wo Oshiete: Although it still doesn't look to have an English translation, I have to mention it just because I think it's one of the few VNs to make the most optimal use of the medium. It uses the music and atmosphere to perfectly get the reader into the head of the protagonist, whose world is increasingly falling into schizophrenic disorder. It's a classic in psychological horror.
3) Swan Song: One of the earlier VNs which got me addicted to this medium. It's a grim story which delves deeply into the nature of humanity. Both the good and the ugly, but especially the ugly.
4) Suba Hibi (also known as Wonderful Everyday): It's the closest thing to a work of post-modernism that the VN medium has got. There's almost too much to say, so in an attempt to keep it simple, I'll just say this. If you have the patience to stick through with it to the end, you'll likely find something deeply rewarding in it.
5) Yume Miru Kusuri: Honestly I was struggling with what to put for number 5. But this was the VN which first got me hooked on the medium of VNs. Aeka's route was probably the first thing I remember staying up all night to read. Having reread the VN a year ago, I can attest that it fully holds up.
