An innovative concept make this game an instant classic even if it is way too short.
The voice that accompany you is very great, it always has a little something to make you laugh or that taunts you. The music from the generic is absolutely incredible.
I have to say that the game is very difficult. This game is not made for everyone. If you do not like to turn in circle to find a solution, this is not for you. There are some places where you will have to repeat-repeat-repeat in order to succeed. You will know what to do but that will require so much precision. There are also some places where you will have no idea on what to do to be able to get through the obstacles. There are several guides that can help you, even within Steam.
Another con is that the game is very short. It took me around 4 hours to complete the game. It contains 19 rooms, which can take between 5 minutes and 30 minutes to complete. There are also the Advanced rooms that you can do, which are basically the same rooms than in the story, but with additional constraints. There are 6 of them. Other than that, there are the challenges, in which you have to use the less portals, the less time or the less steps as possible. This mode does not really interest me, so I will not write on it. Just that you know that this can be done, among others to unlock some success in Steam.
If you want to try something new, try Portal. It is only 10$ and it is often at 50% rebate.