I think we actually agree, so I'm not sure if you misunderstood what I wrote a little, or if I'm misunderstanding your question above, sorry!
Some people still seemed to be wondering what the OP was really asking about, and what she meant by "good." I said I think she was quite clear as to what she meant, and so in the end, the discussions of art quality weren't that relevant to her question, that's all.
Yes, you can only judge whether or not a deck will work for you and give you good readings by looking at it yourself and reading with it! One can only have a reaction by looking at the cards. I disagree with the idea (as discussed generally in the thread) that the quasi-objective "quality" of artwork or amount of rich esoteric symbolism in a deck correlates with whether or not most readers will get "better, more accurate readings" from it, which is what the OP wanted to know.
The discussion had shifted from talking about a person's own reaction to a deck to analyzing how to tell if a deck's art was truly better in the objective, art-criticism sense. As others have pointed out, I might personally enjoy or connect with artwork that is technically, objectively, "bad art". The connection, or ability to tweak one's intuition (as Grizabella put it) is what's important for good readings, not the actual quality of the art. Some readers may need to connect to a deck on an aesthetic level, other readers need esoteric symbolism that clicks with their brain, and for other people even ugly and symbolically spare images can spark their intuition.
My point was only that true art criticism and layers of esoteric meaning aren't relevant to a deck's usefulness
unless that particular reader cares about them. Many do, but some don't!