In order to accurately answer the OP's question, I would need to qualify exactly what is meant by a 'fail.' Are we talking yet another ASM2? As in a movie that has a bad critical rating and continued decreasing profit? Or like a lower tiered success in terms of what Marvel has accomplished so far? i.e. Thor 2, IM2, etc. (Both of those I would consider better than ASM2). I think knowing this makes a difference.
But in general, I think it's safe to say, thanks to Sony's efforts of dragging Spidey through the mud, there's a tremendous amount of pressure on the delivery of this next solo movie. We've seen how a great success, i.e. DoFP, can restore faith and the fan base in a product after dismal movies, i.e. X3 and Origins. Spidey is currently in that same sinking boat. Marvel really needs a winner--a film that is fun, technically sound, and good for the character, to bring back the diminishing bases. I would say anything less than that would be deemed some kind of 'fail.'