Because I want to write for ages does not review here my subjective impressions:
General
+ Lots of fun and "play-through Addiction Danger" - constant exciting
+ Free adjustable language
+ Good music like in the predecessor
+ Many test chambers with new "test articles"
+ Increasing difficulty
+ Sarcasm and irony in the toughest pure form combined with a lot of wit and profundity
+ Low requirements to the computer for great graphics and performance
+/- Part 1 should be known in order to understand everything (especially all references) - the Half-Life universe is not necessary
+/- Playing time is about 12 hours (6 hrs SP / MP 6 hrs)
-Often Relatively easy puzzles
-Wiederspielwert If all Achievements have been made (close to 0 if you have a good memory)
Singleplayer
+ Full really good and extravagant history
Co-op
+ Complete set of tests (for little "history")
+ Many test chambers that actually require teamwork and Timing
+/- Depending on who you play you need patience, especially without voice chat.
Partner, signals not resolved ideal
Conclusion: Fans of Portal 1, it will be unable to leave Portal 2 play through in a few days. The game is just like the previous really addicted to more. Although many puzzles are relatively easy to solve, but what does not spoil the fun.
To play the game in English and without subtitles (English): Tip. The original texts and original voices make it a lot! "To hear" is not one practiced in English it is better to switch to the German language, instead of playing with subtitles.