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.
Before the bossfight I would have given it 8 out of 10 possible points.
The mod looks great, has new ideas and pulls them off quite nicely.
Then the bossfight started and made the whole experience of the mod even better.
I am GLaD that I waited until I have played Portal 2 to write this review. Because now I can say that this mod has the best bossfight from all Portal installments. Seriously, this mod has a better bossfight than Portal 2 and a much better than Portal.
To sum it up: The quality of this mod is between Portal and Portal 2. While it is much better than Portal, it does not come close to Portal 2.
But it is a mod that was released quite a while before Portal 2 was announced, so I'll give it a score as if Portal 2 was never there.
9/10, for a mod that is better than the brilliant game it was made for.