There are a few ways to "look" at Half-life 2, however in my opinion it stands up in all of them - feel free to disagree.
In terms of First Person Story telling, Half-life 2 remains the champion. It's story is less told through lazy cut scenes and more through the world and incidental details present therein. The lack of children and pets, the deep philosophical ramblings that bombard the citizens, even the furnishings in the houses tell a story better than some pathetic shock-value opener. The trips to Ravenholm and Nova Prospect towards the middle of the game dip the world in a dark and terrifying vibe that supplants most full fledged Horror titles because it doesn't SAY anything. It just puts the details in the world and lets them speak for themselves.
In terms of Gun Play, Half-life 2 isn't as visceral as it's modern day counter parts, however the moment-to-moment gameplay is still well ahead of basically everyone in the industry save for perhaps Halo. The A.I. drives the scenario based combat, meaning it reacts to the player and allows them to employ wildcard strategies that the A.I. adapts to. Most modern shooters all but ignore A.I. in favour of scripted battles - Half-life 2 weaves it's scripting amongst the on-the-fly scenarios. The first real battle against the Combine drop ship on the freeway, the fierce firefights through the City during the game's final chapters, and even the moment-to-moment use of the gravity gun allow for a more varied and immersive experience.
Lastly, it's setting is incredible, though lacking the awe of something akin to Bioshock's Rapture. It's eschews the realism of the modern shooters, leaving behind your glocks and M14s for more inventive and "fun" firearms. Instead of simply killing "The Non-Americans" as is the norm for the industry today, you're fighting monsters and alien soldiers, not because they "Hate Freedom for [reasons]" but because they're simply trying to wipe out humanity, turning them into zombie soldiers for their army. It's escapism, pure and simple - and for the dreamer in me, it wins out over the endlessly boring Military Shooters of today.
All my opinions, of course.