Portal: Unity is a mod for the Valve game "portal" with almost everything revamped. New story levels, New textures, redesigned portals, new protagonist, new antagonist and hopefully much more to come.
This is one of the best mods I've played in a while. However, there are a number of issues that prevent it from being a truly solid game.
a) In the lobby (escape03), there's a metal detector that activates a red field guarding one of the hallways. If the detector is triggered before the boss battle, on the way out the player is trapped on the other side of the field. Portals cannot be used, as all the nearby walls and floors cannot be portaled. This makes it impossible to complete the game normally, even using noclip.
b) The launch video is encoded with the Xvid codec, which isn't installed by default. This results in an ugly error message while the video is supposed to play. While I probably should install a codec pack, it would be a good idea to use a codec that ships with Windows.
c) As another reviewer pointed out, magic illumination breaks immersion. It would be a good idea to add some fluorescent lights to the hallways and chambers à la Portal.
d) The voice acting is much better than a number of other mods, but it ends up being almost completely unintelligible. Adding subtitles is an absolute must - otherwise it's very difficult to tell what's going on.
e) The final boss battle was neat but it was quite counterintuitive - I initially missed the yellow lever by the elevator and assumed that the goal was to redirect the rockets, as in the Portal boss battle. It wasn't very hard to figure out after that was sorted out but it might be a good idea to e.g. make the lever more obvious.
f) While the map design is quite good for most of the game, it seems to suffer from a lack of refinement toward the end, especially after the boss battle. The hallways are too geometric and undetailed, and the elevators are like the ones from Half-Life 1.
g) Finally, it might be nice to dress up the menu screen a bit more, such as by adding a graphical logo.
I'm only nitpicking this so much because it's such a promising mod - unfortunately, a 1.5 update is sorely needed.