Portal: Alive and Kicking is a free mod that plans to recreate Portal in Portal 2
For those, like me, who only need the merest reason to play Portal again, keep an eye on Portal: Alive and Kicking. It's "a full remake and re-imagining" of Portal 1 in Portal 2's fancier iteration of Source. The free mod that's been passed through the latest batch of Greenlight approvals, and has the confident endorsement of Jeep Barnett, Valve designer and co-creator of the proto-Portal student project, Narbacular Drop. "Every tile on every panel has been revisited with loving detail," he writes. "Not only have the visuals been updated to match Portal 2, but the weaker puzzle cues have been improved."
The mod also includes a new set of advanced maps based on Portal chambers 13-18, but with "all new puzzles and set in the "Old Aperture" visual theme seen in Portal 2." The adaptive soundtrack has been expanded and Portal's original advanced maps have been recreated in the Portal 2's ruined Aperture aesthetic. It looks a bit like this.
I was a bit skeptical about fan-make remakes of old games until I played Black Mesa: Source. The act of recreation through the lens of intense fandom added dozens of loving touches that enhanced Valve's original vision for Half-Life. See also, The Dark Mod, which did a great job of capturing the magic of Thief. Hopefully Alive and Kicking will do the same for Glados et al.