It's well known that Half Life 3 never came out, but I was surprised to know that "Half Life 2 Episode 1" was an episodic sequel so it is basically the 3rd game. However, this episodic sequel was meant to have 3 parts, but the final part never came out. So Half Life 3 and Episode 3 never materialised, which surely adds insult to injury.
Alyx didn't feature that much in Half Life 2, but here she is at the forefront, teaming up with Gordon Freeman throughout the game. A companion makes the adventure feel different, but makes it even weirder for Gordon to be a silent protagonist.
Episode One picks up right where its predecessor left off. The initial level is a bit bland which sees you stabilising the core at the citadel. Just like at the end of the previous game, your gravity gun becomes overpowered allowing you to pick up or blast enemies without much thought. Once the game progresses, there's some better ideas like the underground horror segment requiring you to shine the light on enemies otherwise Alyx cannot attack.
The episodic format does mean that Episode One is a shorter experience, but the five chapters are tightly paced, so still delivers a quality experience.