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.
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.