I voted for Gabriel Knight (1 & 3) as the only games on the list I've completed twice.
As Collector pointed out, I find the lack of Sierra games disturbing.
The Quest for Glory's have been the games I've most replayed, 4 or 5 times each save for QfG5 which I've only finished twice. Then there's LSL 1, 3 & 6, SQ 5 and PQ 1 & 2.
Outside of Sierra, Indiana Jones and the Fate of Atlantis and Sherlock Holmes: The Case of the Serrated Scalpel are the only ones I can think of off the top of my head.