Matheson does pretty much everything he can to ensure the protagonist is hard to sympathise with for most of the book. He is consumed with rage, bitterness and fury at the hand the universe has dealt him. He is entirely self-absorbed, lashing out at his friends, family and the world. No one understand what he is going through, they all laugh at him behind his back and pity him to his face. He feels belittled in every way, not just physically.
So, I can see why many people might dislike this book. You feel more sorry for his family who must endure his tantrums than him having to endure his plight. You almost want the spider to catch him just to put him (and the reader) out of his misery. But it's all necessary in my opinion. Scott is on a journey, has to overcome his inner demons before he can deal with those around him.
The narrative is split between his plight in the basement when he is less than an inch tall and his days are a constant struggle to find food and water whilst escaping the menacing black widow spider that is intent on making him it's next meal, and frequent flashbacks to his recent past at different moments after becoming afflicted with his condition. This was a good thing because the narrative of his plight in the basement would have become a little monotonous if not tempered with these recollections which serve to gradually fill in his background, what caused his condition and how he came to be stranded in the basement.
The science is a little hokey so it's best not examined too closely but that's not really as important as the psycological study of the protagonist. As if his condition wasn't bad enough, he is tortured by a mounting libido that can't be satisfied.
So, another hit then for Matheson who is yet to let me down. I look forward to seeing what else this author has to offer.