Had a quick go this morning. Graphically its very rich, on par with CS:S which was to be expected. The sounds are very good with a richness thats hard to explain.
Some nice touches are the ability to switch from auto to single shot and also iron sights for some of the weapons.
Game play hasnt really changed a lot. Heavy machine guns can be deployed on ledges etc, and the rag doll physics are pretty cool.
If you havent got HL2 then never worry. If you have HL2 then get this. A clan match in this game would be awesome.
Fairy