I just finished Half Life 2: Episode One, and the feeling I have is one of satisfaction.
The game takes place right at the end of Half Life 2, when the core of the citadel explodes. The game begins when some one-eyed aliens save you from the explosion, and the mission is to rescue the humans left in City 17.
Throughout the game you are accompanied by Alyx, who helps you throughout the game by eliminating enemies and giving you clues about what to do.

The graphics in terms of settings and characters are practically the same as those of Half Life 2, which does not mean bad by any means. An aspect that may have improved a lot is the issue of light treatment, since there are moments in which the Sun reflects on some tiles and it looks very good.

The conclusion is that the game does not disappoint if what you are looking for is, like me, a continuation of HL2, which leaves a lot of doubts in the plot, especially at the end. This expansion also leaves more doubts than clear things, but it is something that must be assumed since there are still two more episodes to go. The only drawback: The duration; In 5 hours or so it’s over.
