Allow me to proudly present you
Opposing Life2Life, the Gold Source of Goldsource mods.
If you click the link nao, you will see a list of 22 mods that this mod was built upon. Since they credited those other mods, there is no need to go STOLEN STOLEN or whatever spam on their page. Well, actually they didn't credit
all of the mod contents they used (e.g. They Hunger, Point of View, Redemption, etc.) so do what you will.
So what the EFF exactly is this mod? Well, imagine going into opposing force and typing "map c0a0". That is more or less what this mod tries to achieve. You get to play vanilla with Opposing Force Coding.
BUT WAIT A MINUTE! This mod offers more than just that. Didn't I just said this mod is built on 22 other mods? Yes it is. So, if you play thru this mod, not only will you see monsters from OP4 (like gonomes and shocktroops) but you will also get new weapons from OP4. So, in a way this is just like playing Half life with OP4 code. But in a way it is better.
Sprawled throughout the mod are nonsolid prop models placed almost everywhere. Some are nice to look at. Some are generics that can be gibbed. And some are annoying because they block my view and the grunt behind it can take potshots at me. AR time.
The mod quality is discouraging at first impression. They start out from the opening cutscene of Visitors, which was badly linked with the opening of blue shift, which in turn is badly linked with the opening of vanilla HL. So just start a new game at c1a0 and you're all set.
The first thing you notice is that your colleagues are no longer clones of five certain individuals. You will definitely see some familiar faces here and there, but unfortunately this means that later on you will see a variety of bodies around the complex. Sob.
Storyline plays out normally in this mod. That is, until you take your unpaid vacation to Xen. At Xen, Gordon will be in entirely new places that will look familiar to you. This is not a grammar error, I really mean it that way. So then after you realign the focal transmitters, Rosenberg tells you to hurry and return into the portal. But guess what? That cheeky bawstard redirected the portal right into Nihilanth's factory. Damm it.
So go ahead and grab this mod and see your favorite mods make their cameo appearances in vanilla HL. Just remember that the file size is almost the combined file size of all these mods, so it will be obese. Now go and throw a displacer ball up Nihilanth's face, and enjoy the fireworks.