All romantic comedies follow the same plot thread. If you've seen on RomCom, you will be able to call out what will happen next in every other one: guy meets girl, they get together and have their romantic comedy, something happens to disrupt the relationship, they reunite before the end credits.
No Strings Attached follows this thread. Natalie Portman is fantastic. Is there a role that she cannot play exceptionally? Ashton Kutcher, on the other hand, plays the same exact character in every movie he's in.
They meet at camp as young kids and then hook up again as adults, agreeing only to have their relationship based on sex and no emotional attachment. As is the case for every Kutcher character, he falls in love with the girl and is the poster boy for charm and chivalry. Portman's Emma freaks out and it looks like the relationship has reached it end.
I will admit that I did chuckle a number of times during this movie. The humor feels real (most of the time) It does suffer from the cliched "given" scenes and lines of every romantic comedy but, when it's a date-night movie, these things can be overlooked.
Portman made this movie following her turn as The Black Swan so it feels like she did it to come down from the dreary world and relax into a mindless fun flick. Kutcher only wants to play the simple, every-woman's-dream in every film he's in.