This is a great question and the truth of the matter is that this topic is very debated. So, it really depends on who you ask. Here are the two main views.
There are some people that say that the intention of the artist is central in appreciating art. So, these people will try to find out all they can about the artist. They will also try to find out about the historical and cultural context in which the artist lived. By looking at this information, these critics believe that you can learn so much more and appreciate the work of the artist in a more sophisticated way.
There are others that say that intentions do not matter as much. Why? Beauty and appreciation is in the eye of the beholder. More importantly, in a postmodern world where all things are pretty much relative, intention does not hold too much weight. What matters is our interpretation of things. In other words, the locus of meaning and appreciation is with the critic not so much the artist.
With this said, in my opinion, the truth is probably somewhere in the middle.
Of course it's important to take into account the intention of the artist in why they created the piece because that's obviously what the artist is going for; however, there is a reason why everyone thinks differently, and sometimes what the artists intent is isn't the same as what the audience is thinking.
The intention of the artist is especially important when looking at the conceptual arts, for example: "Wrapping" in the style of Christo and Jean-Claude provokes the viewer into the artists' intentions.
Printmaking is another area where the intention of the artist defines what an "original" print is. "The Scream", as an example, was not only a painting, but was also several lithographic print with different artist's intentions for the work to be created.
I think that if we are viewing art, we naturally ask, "Why?" And, isn't that always an intention? it's a result of the artist's own creative process and that intention expressed in the art produced.
So, yes, the intention of the artist is important to consider. No critique would be complete without this consideration.