Resident Evil 4 went through a lot of changes between the time it was first shown off in 2001 to the time it was released in 2004. The finished product is a classic, but we're now getting a chance to play through an earlier, cancelled edition of the game, which has been rebuilt by a fan.
Capcom went through at least four versions of Resident Evil 4 before it was released, three of them scrapped (but not before being shown off at TGS and E3) for various reasons before Shinji Mikami was brought in to deliver the edition of the game that we actually got to play.
A fan by the name of ShiguWorks has looked very closely at one of those cancelled versions (known as Hallucination) and, using footage from its E3 2003 demo, rebuilt sections of it.
This is what the original E3 demo looked like:
While below is footage from ShiguWorks' fan recreation:
When it's done, he'll release it as a standalone "fan game" called CODE:Madman. In the meantime, you can check out a short playable demo that you can grab from here.
Resident Evil fans may remember this isn't the first time this sort of thing has happened: A few years back we got a playable version of Resident Evil 1.5, a scrapped, earlier version of Resident Evil 2.