I don't think she is seen as a serious actress anymore because of the roles she chooses and is known for.
Since Vicky Barcelona (2008) she has done:
The Spirit (2008)
Iron Man 2 (2010)
We Brought A Zoo (2011)
Avengers Assemble (2012)
Under the Skin (2013)
Don Jaun's Addiction (2013)
Captain America: The Winter Soldier [pre-production] (2014)
The Avengers 2 [rumoured] (2015)
Unless she fits in a few decent roles she is going to become known for the Black Widow role and not as a proper serious actress, especially if the rumoured Black Widow film gets made in the future.