Black widow in Iron Man 2: Subtle, secretive, concealed her identity quite well, come the end game, oh shit she's a hard case, AND on our side
black widow in The Winter Soldier: Painful reminder of the nature of shield and the spy business in general, but when shit hits the fan, stands with captain america through hell and back, risking her life countless times for the good of humanity.
Black widow in the avengers: Eye candy, only purpose is to pine like a love sick school girl, beat people up in lingurie and just be there as a token female.

Thus further proof that Joss Whedon is a cancerous arse tumour of a writer.

Stop...your triggering my ptsd. Fuck you drake..