While Half Life 2 isn't perfect, it does something so many games nowadays are afraid to do: Make you think.
My favorite part of the game was the puzzles and the general theme of rewarding players for using their heads. Nowadays, games that make you think are few and far between, so it was very refreshing to play a game that isn't just about running and gunning. Half Life 2 will slow you down, whether with a puzzle or trap and make you solve the environment puzzle before progressing. With regard to this, it does a great job of pacing and designing these puzzles so that they are not too challenging, not too frequent, and rewarding to overcome. They also do a good job mixing them up so you encounter a variety of different environmental challenges. Most of the puzzles involve physics of some kind whether that be balancing the weight on ramp, using planks to get across acid, or searching to find an item. The variety is nice, and it gives the game a chance to showcase its renown physics engine. (I will say that they're trolls for hiding the battery under the bathtub)
Aside from the great puzzles and story, Half Life 2 doesn't really have any weaknesses which is a strength in itself. Personally, I wasn't overly impressed with the combat, control, or graphics, but they are all solid enough where in the context of the overall game, they come together nicely. I would have liked to see some more variation in the weapons between the base game, especially between episodes By the end of the game I was pretty tired of the assault rifle, SMG, and shotgun as those will make up a lot of your kills. The gravity gun is a really cool weapon that again rewards players for thinking in saving ammo and showcases the realistic physics. Most people would probably disagree with me, but I wasn't a huge fan of the control. I just couldn't shake the feeling that everywhere I went I was sliding around. It didn't feel right to me and just felt slippery.
Its hard to review a game like Half Life 2 because it truly has no flaws, there are only things you like more and things you like less. To sum it up, it had outstanding puzzles, an interesting story and environment, solid combat and enemies, average controls, and a badazz crowbar.