I wouldn't say I'm in the know about VNs by a long shot, but the few I've played I've quite enjoyed.
Number one would be the Ace Attorney games. I've played every single one and enjoyed each immensely. Their quality is varied but don't fall below 'average' and the majority are 'great' to 'above average'. The AA Trilogy is the best place to start as I think they are best played in order of release. The games are pretty long averaging about 30 hours each and there are no alternate endings.
I've also started playing the Zero Escape Trilogy and highly enjoyed the first game. The second game is next in my queue when I finish up a couple current games in my rotation. I've heard often is even better than the first, so I look forward to that. It took me 16 hours to get the 'true' ending in the first game.