There's not really much left to say about Portal that hasn't been said - the first-person shooter as a puzzle game was a great new concept at the time, and mixed with the sterile, clinical scientific environments and AI voice assessing your every move that both became delapidated and deranged over the course of the levels was a very memorable experience. The ambient electronic music pulls a lot of the weight too, keeping you in the zone when you're puzzle solving but not afraid to fully disturb you whenever you discover something the facility didn't want you to see.

It's overall a great game that can be experienced in a few hours and I still go back and visit it occasionally.