In all honesty, it just isn't that great.
First off however, I would like to say I really enjoyed the combat and the physics. This is what made me finish the game. I would say they make for satisfying yet shallow kills.
I played the first half life about two months ago after getting portal for free. I decided that if valve could make a game this ingenious, surely half life is even better. So I played half life 1 and loved it. Then I bought half life 2 and all I can say is that the story was dull and the dialogue was the cheesiest I have heard in ages. Nothing except the combat reminded me of the original half life.
The graphics and physics again, made the game fun but I just can't get over how bored I was half the time.
Maybe the fact is, that I am spoiled with all the new games. I played crysis and loved it and this game feels like a lame version of crysis. Gordon freeman never talks, there is no sense of magnitude or realism beyond the physics which sometimes don't even work that well.
If this is your first time playing a FPS, you may like it a lot. However, for anyone who has experinced Modern Warfare, Gears of War, Halo, and Crysis, you will be sorely dissapointed by boring visuals and annoying characters.