There are a lot of VNs I like. It would take a lot of time to write about them all, so I'll only list some of them.
Kara no Shoujo - it was one of my first visual novels and, although gruesome scenes often shocked me, I found the plot extremely interesting, liked characters and gameplay. You really had to think there to not get a bad ending.
Amnesia - my second otome game. I fell in love with characters and I really liked the plot. Also, every character's route had it's unique features distinguishing it from other routes - you had to find a culprit in one route, you had to solve math problems in another, you had to survive in the next and etc.
Black Wolves Saga - I liked music and the dark setting of its world. Also, I just like to observe crazy characters, it never gets boring with them. I wish the main character wasn't that naive, though. She could do nothing but be swept by the course of events most of the time.
Gekka Rouran Romance - I found all love interests extremely odd at first (a kid, a woman, a teacher, brother and a couple of corrupted rich boys - nuff said). However, learning these characters' backstories was extremely interesting and made me change my opinion about them in the end. Also, the gameplay was pretty unusual - you could pursue either pure love or passionate and a bit corrupted one.
Sachi no Tenbin - mostly because I like yandere. I also found the main heroine very likable. Also, if you receive a good ending with one of the guys, you get to see his point of view explaining his backstory, his inner thoughts about the heroine, his reactions to her words throughout his whole route. It was the first time I saw such long and detailed PoVs in an otome game. Also, it showed thinking process of yandere - a very interesting material for me.