So half life 2, eh? Lots of people have been waiting for it and that includes me. I'm gonna just tell you a few reasons why.
Firstly, a whole new feeling - being outside! In the first game you were stuck inside for 99% of the game. Now you have huge areas to run around.
Secondly, the new physics engine. The engine used here is the ragdoll physics system. This is hilarious as dead bodies don't stick through walls, instead they lean up against them.
Thirdly, new weapons! There were some great ones in Half Life 1 but in HL 2 it's even better and they all look very realistic and believable. A funny thing to do is use the shotgun on the combine soldiers! They go flying!
Finally, the graphics. They are stunning. I put my graphics installation on minimum and they still looked incredible. The people that you meet look so real and they act and speak as if they were real. This is one of the games major strong points!