Portal: Revolution is the first Portal mod that felt very well-polished to me. The puzzles work, no weird cheesing, and the achievements are well-incorporated as well.

I wouldn't say this mod was difficult compared to other mods, but it was more atmospheric and a lot less frustrating. A nice, short story with plenty of puzzles. Revolution even features new mechanics, which were fun and refreshing. I wish there was a little less "navigate the facility", but overall a pleasant experience.

The voice-acting was pretty good, too. Although the story was clearly written from fans' viewpoints, it fit well into the Valve universe.

I recommend Portal: Revolution to anyone who is in for a refreshing puzzle experience after having completed the main two games.