Groundbreaking, a true achievement from Valve.
I know Source engine has had its moments, its still in my opinion one of the best, sharpest and most well-established engines to date. Episode Two just took it to a WHOLE new level.
The textures in the game have been given some serious consideration. Everything looks and feels real. When inside the cave area, there's a lot of water and the walls have this shiny texture to them, indicating that they are moist/damp.
The lighting is what truly blew me away. Shadows are cast very realistically and so far the game has a very eery and dark atmosphere. You really find yourself immersed in the experience.
The sounds are just awesome. I played the game with 5.1 on a X-Fi XtremeGamer Fata1ty Pro soundcard. The sounds are very realistic and create one of the best atmospheres I have experienced in a game today.
The performance and optimisation of the game has, as we would expect from Valve, come through with flying colours. I was able to max the game entirely with 1680x1050 resolution and 16xQ AA / 16x AF. Granted i ran the game with a Q6600 @ 3.6ghz and SLI 8800 GTX's, my frames were very high, averaging well above 70fps, clearing 100 on more than several occasions. I would not be surprised if, when a test is run, I average 90fps.
Lastly, the story so far is very deep as usual but gets you a lot more involved. Granted I have not completed the game yet, they really have you interacting with others. I have just helped a two-man squad fight off a MASSIVE hoard of ant-lions with the help of some well-placed proxy mines and some moveable sentry guns. Once the arse-kicking gets heavy, our fellow Vortigaunt friends show up to add some light shows and serious carnage to the battle. I had to force myself to stop playing this game so I could sort through all the screenshots I took and write up a short review.
10/10 in my opinion. Honestly.