I am not saying that portal 2 is a bad game. I am only claiming that portal 2 is a bad puzzle game.
1- Puzzles are too easy:
Portal 2 has really easy puzzles. Nothing in that game made me think more than 5 seconds.
2- Mechanics are abandoned without exploration:
There are lots of stuff in portal 2. A lot of components. But these components are just abandoned without a through exploration.
3- A high execution time/thinking time ratio:
Even though you understand what you have to do in 2 micro-seconds, You have to spend minutes executing the solution. This is considered bad in puzzle games. If there is a long execution, There must be a lot of thinking the player does before that execution.
4- Small touches could have made the game better:
A lot of the puzzles may have used some small touches to become better puzzles. This points at poor design.
Portal 2 does a great job in introducing it's puzzles and making it hard but not too hard to understand what's going on. Portal 2 uses a system that makes the game easy to understand and this system is why it's such a great and beloved game. The system goes like this, You have a mechanic you want to show the player, What you do is give them the mechanic in a safe zone, Where they can mess around with the mechanic and understand how it works, Then start to add threats in addition to the mechanic in order to test the player with what they learned whilst messing around with the mechanic, The Portal series is great at doing this and it's one of the reasons the games are so popular!
I for one found the puzzles the right difficulty, A few times I had to look up the answers and I think that VALVe tried to make sure that the game was able to be played by anyone.
I can't think of a single mechanic abandoned. Please elaborate.
I didn't find the puzzles too long to complete, Because I did it step-by-step, Which is I think the intention. VALVe focus tests to a fault and ensure that the game is incredibly well balanced and has a fantastic story with action and humour. To quote Yahtzee "Portal is great and if you don't think so you must be stupid". I don't think you are stupid, I just like that quote.