I think my first adventure was Leisure Suit Larry 2. I went on to play lots of Sierra adventures until I bought three games in a row which were intolerably short, including one that took me about 4 hours of not particularly intensive playing to finish. After that I vowed I would never again buy an adventure game.
Until, that is, I played the first Monkey Island, which I picked up in a bargain bin for about $10. It was a bit out of date at the time, but all the things that Sierra adventures did wrong, Monkey Island did right.
I decided to give adventure games another try, but since that day I have not bought a Sierra adventure. Not even Gabriel Knight.