I give it a 9 out of 10 because i felt there was some areas where it could have improved. Overall it was better than the first. I glad you got the dual portal gun faster and it was longer because Portal was short and i finished it in like an hour or 2. I loved the physics and the new tools and stuff you get to use.
SPOILER ALERT SPOILER ALERT, i liked how you got to see the old Aperture science's and what they did SPOILER ALERT OVER
I like how they trained you to use the new tools but it could use just a little improvement and some parts i got confused on what to do but after looking for about 2 mins i figured it out