Darkness... My body hurts! Or is it my brain? The explosion! I remember it now. Maybe I'm in a coma? Or even worst, I may be already dead... Everything is so confusing... Zombies, monsters and ghosts from the past are filling my mind... Oh God, so many memories mixed with my dreams! I can't even distinguish them anymore. What if my entire life was just a nightmare? But it felt so real... Wait, what's that sweet voice? Sounds like a nurse! THAT is part of reality, I am sure. Now if I could just concentrate on this voice and try to wake up...
There's a reason why this is one of the best Half-Life 1 mods. Not just because it's a game about killing zombies - the models, maps and weapons are all amazing. Adding to the fact that this trilogy was released by PC Gamer years ago proves that some mods can become successful with someone/some people who have the sheer amount of dedication and attention to game quality.
The first chapter is more or less a survival game - using your melee weapons to mow down zombie walkers although through the remaining chapters, you'll have access to more powerful weaponry. Since this is more or less a survival game, you can't afford to get hurt a lot since you'll not only face zombies, you will also face other horrors such as They Hunger's version of the headcrabs, dogs and re-animated skeletons.
Boss battles are handled well, especially the last battle between you and the infected sheriff - Both of you are trying to blast each other out while riding on you respective helicopters.
So if you are still reading this and you haven't even played the game yet - please DO SO and you will not regret it.