Polished quality game from Valve that holds true to the original and introduces new puzzles with a longer campaign.
The story and humour take a forefront and are definitely accentuated by the superb voice actors. They include the original female voice and a new male character with a british accent which both have their own personalities and moments in the game. While in the previous game the humour was kept a little more subtle, but in this game it is very much at the forefront and is a welcome change.
There are several new gameplay elements that have to be used with the portal gun to solve puzzles, such as three types liquid goo that must be placed on surfaces, lasers and reflector blocks, electric walls/bridges, and a warp tube. In the later levels sometimes you can get stuck trying to solve the level using all these new things when you realize all that is needed is a simple portal. Can be confusing at times.
The maps are well made, but the game is really pushing the source engine to its limits. The engine is pushing 8 years by now, but graphically they really did the best they could with the engine. As a consequence there are loading times almost every few minutes. After every puzzle there is a loading time. The maps differ greatly, during the start and other phases you get the typical test chambers, but later on you are navigating larger open areas with your portal gun, and there are downsides to this as I will mention in the next paragraph.
There are a couple quirks that I felt interrupted the flow of the game. Firstly the larger open areas were an interesting change, but they can be frustrating and annoying. It turns into puzzle solving to basically a pixel hunt to see where the white wall is to place your portal to continue on. Other times the flow suddenly changes from small map, where you were solving smaller puzzles using more advanced techniques, to a large map where it expects you to use more basic techniques to continue. But since you were used to the advanced mindset you over complicate things and only confuse yourself until you realize the simplicity of the solution.
The game has extremely simply levels mixed in just to show you the purpose of new gameplay elements such as the liquids and etc, and you use them always in the same way. However in several stages in the game I found they want you to solve a puzzle in a way that has never been done before and they expect you to know how to do it or that it is even possible. For example using a laser to cut through the side of a bunch of tubes. It took me 5 minutes of running around trying to pixel hunt white areas to place portals and using the gameplay methods used before until I stumbled upon the stupid laser cutting thing. Another time you are expected to know to interrupt a laser beam to shut off another device on the map, but prior this was never used in the game so it left me stumped and forced me to read the walkthrough. Overall these couple parts are not rewarding but frustrating.
Other than the quirks the game offers some variety of difficult and easy puzzles and the new gameplay elements mix things up. The environments and voice acting are both excellent. The story is intriguing and the humour is funny. Unfortunately there is little replay value in the game, since once you have solved the puzzles there is little fun in replaying them over. There are no challenge maps like the the previous game, which is disappointing. Worth playing definitely.