Gordon is brought back into the world by the G-man and finds Earth to be taken over by an alien race, and Gordon must help the Resistance take back Earth.
Brilliant plot and story with influences from the novel Nineteen Eighty-Four. The area also has references from many Eastern-Europe countries, via signs that are written in different languages besides English (such as Russian, Romanian, etc.), and that there are also more areas to explore within that world such as a drained coast, zombie infested town, prison or an alien fortress. Rather than taking place in a western setting, such as the U.S., or confined in a large facility, the game takes place in Eastern Europe, which is a really nice and interesting idea. This includes Isaac and Eli who were both scientist that worked at Black Mesa and were there during the events of the first game.
Because the game is more focused on story, there are actual characters in the game. More backstory about the protagonist, Gordon Freeman. Instead of the same copy-paste scientists and security guards that Half-Life 1 had, there are more types of NPCs and even new characters who are extremely likable. It also stands out from other FPS games that use them because most of them are just "go there and press button or destroy something with this to progress", here in this game most of these puzzles actually feel like physics or environment interaction is involved. Great puzzles that are all physics based, which makes sense since Freeman is a physicist. These graphics still are great to this day.
The game has revolutionized graphics and physics due to being made in the Source engine, which was capable of more emotion in characters and beautiful environments that look lifelike.