19. Portal (17)
Probably only down this far largely because I'd play it's sequel if I wanted to revisit this type of game, this may be the game that makes me give the FPS a second chance (computer aiming seems far simpler than console for someone poor at multitasking). The wonderful physics puzzling of the portal gun progresses nicely, teaching you all of the different things you can do with your "weapon" at a reasonable pace. GLaDOS is nearly a perfect character (honorable mention to the turrets) with the writing for her character, and the song in the end credits alone is almost worth the price of the game when its discounted (often). The game didn't overstay its welcome with the part after the test chambers becoming less straightforward but still using what you had learned. As a result of how good this game is, I couldn't wait for the sequel and the addition of new mechanics and forced me to buy my first gaming computer.
Primarily an RPG player but have interest in any game that will make me think.