Indeed, Portal much more than a technical gimmick, it’s a puzzle game that excels through extremely well tested level design and minimalist story development. Portals are a very powerful feature / action with a large playspace of possibilities. They carefully avoided the common mistake of thinking this in itself = fun, but instead they figured out the narrow path of interesting levels and scenarios to balance the teaching/achieving curve to make a great game. 20% gimmick, 60% level design, 20% humorous story told through the environment.
Yes, I’m a fan.