I have missed many adventure games on Amiga and PC simply because I am not very good at this type of game. Reading this thread it seems there are many games I'll have to try out.
I had the pleasure to play Days of the Tentacle a long time ago. It is adventure gaming's finest hour with its (il)logical puzzles to solve. I still must have that game on floppy discs...
I always loved horror-adventure games and Darkseed on Amiga is definitely my favourite.
Walking around a Victorian mansion, discovering secret rooms and chit chat with people from the local village are some of the actions which make this game worthwhile.
For PC I bought the sequel, creatively named Darkseed 2, on budget which is despite speech and high-res graphics a mere shadow of the original.
Hmm, I remember I quite liked Sierra's Phantasmagoria too when I borrowed it from someone for a couple of weeks. I don't know whether it was the lack of decent actors or difficulty why I liked this game so much.