Portal: Prelude, as its name implies, is an unofficial prequel to the game Portal. Its story revolves around the pre-GlaDOS epoch way before she was plugged in. Back then, test subjects were still monitored by real Aperture Science employees, a tedious, dull, and repetitive job. One of the reasons why they decided to build a great artificial intelligence that could both replace them for these complex tasks and also take responsibility for many other functions within the complex while competing with Black Mesa's superiority. All employees of the Aperture Science complex are now eagerly awaiting GlaDOS. A little too eagerly maybe, as the unfolding events will tell... This game is totally free. It offers a bit more gameplay hours than the original Portal, with 8 chapters, 19 test chambers, 48 challenges, 6 advanced maps, a brand new storyline and more than 400 lines of English dialogue with dozens of subtitles languages.
This review may contain spoilers
This mod is very impressive. The voice acting is performed by a machine but it is ok. And scenario is quite good. The music used matches the ambiance of Portal and it is nice to see some humans in Portal.
However, this mod is really really HARD! It took me 3 days to finish it while the original Portal was finished in less than 1 day for me.
Spoiler Alert:
There are 19 test-chambers with gradual difficulty and you will have to use some skill that weren't needed in the original game like crouching while teleporting to jump further. I don't know how you can expain that there is more turret in the complex and why GlaDOS is much more powerful in the Prelude than the original game. It makes the mod very challenging. I don't know how many time I died before beating GlaDOS with these buzz-robots from Half-Life 2 following you everywhere. (You don't even have a crowbar to defend yourself). Anyway, It was fun.
Congratulation and thank you for this great mod.